Method for the production of plastic lenses

ABSTRACT

Method, for making a plastic lens. The method includes disposing a liquid monomer or a monomer mixture and a photosensitive initiator into a mold cavity and directing ultraviolet light to act on the lens forming material in the cavity to produce a lens therefrom.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.642,614, filed Jan. 17, 1991, which is a continuation-in-part of Ser.No. 425,371, filed Oct. 26, 1989, which is a continuation-in-part ofSer. No. 273,428, filed Nov. 18, 1988, now U.S. Pat. No. 4,879,318,which is a continuation-in-part of Ser. No. 021,913, filed Mar. 4, 1987,now abandoned, which is a continuation-in-part of Ser. No. 823,339,filed Jan. 28, 1986, now U.S. Pat. No. 4,728,469.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods, apparatus andcompositions for making plastic lenses.

It is conventional in the art to produce optical lenses by thermalcuring techniques from the polymer of diethylene glycolbis(allyl)-carbonate (DEG-BAC).

The polymer of DEG-BAC exhibits desirable optical and mechanicalproperties. These properties include high light transmission, highclarity, and high index of refraction together with high abrasion andimpact resistance. These properties in the past made DEG-BAC one of theleading monomers in the manufacture of high quality lenses, faceshields, sun and safety glasses. Other properties of DEG-BAC, however,such as its slow rate of polymerization, make it an undesirable monomerin the manufacture of these items. Moreover, DEG-BAC, without anyadditives or co-monomers, produces a hard but somewhat brittle polymerthat is very prone to cracking. In addition, DEG-BAC, without additives,tends to adhere tightly to the lens forming molds, often leading tocracking of the molds.

In addition, the thermal curing techniques for polymerizing DEG-BAC toproduce optical lenses have several disadvantages and drawbacks. One ofthe most significant drawbacks is that it may take approximately 12hours to produce a lens according to thermal curing techniques. A lensforming mold, therefore, can produce at most two lenses per day.

Moreover, thermal curing techniques employ a thermal catalyst so that apolymerizable mixture of DEG-BAC and catalyst will slowly polymerizeeven while refrigerated. The polymerizable mixture therefore has a veryshort shelf life and must be used within a short time or it will hardenin its container.

Furthermore, the thermal catalysts utilized according to the thermalcuring techniques are quite volatile and dangerous to work with, thusrequiring extreme care in handling.

Curing of a lens by ultraviolet light presents certain problems thatmust be overcome to produce a viable lens. Such problems includeyellowing of the lens, cracking of the lens or mold, optical distortionsin the lens, and premature release of the lens from the mold.

The present invention is directed to methods, apparatus and compositionsfor making plastic lenses that overcome the disadvantages and drawbacksof the prior art.

SUMMARY OF THE INVENTION

The present invention provides methods, apparatus and compositions formaking plastic lenses., such as optical lenses for use in eyeglasses andthe like.

In one embodiment of the present invention, a method for making plasticlenses is provided in which a polymerizable lens forming material isdisposed in a mold cavity defined in part between a first mold memberand a second mold member spaced apart from each other by a gasket. Raysof ultraviolet light are directed against either or both of the firstand second mold members or the gasket. In a preferred embodiment, thefirst and second mold members are cooled. In another preferredembodiment, the ultraviolet light is filtered before it impinges oneither or both of the first and second mold members.

In another embodiment of the present invention, an apparatus is providedfor making plastic lenses which includes a first mold member and asecond mold member spaced apart by a gasket, wherein the first andsecond mold members define a mold cavity. The apparatus includes agenerator for generating and directing ultraviolet light against atleast one of the first and second mold members. Alternatively, theapparatus includes a generator for generating and directing ultravioletlight against the gasket. The apparatus may also include a means forpreventing the transmission of ultraviolet light through the first andsecond mold members. In addition, the apparatus may include a filter forfiltering the ultraviolet light. The filter may be disposed between thegenerator for generating and directing ultraviolet light and the firstmold member, and between the generator for generating and directingultraviolet light and the second mold member. The apparatus may includea fluid (e.g. air) distributor or a liquid bath for cooling the firstand second mold members.

In another embodiment of the invention, the lens forming material may becooled at relatively low temperatures while being exposed to ultraviolet("UV") light. The lens forming material may be cooled by directingvarious flowrates of cooling air towards the mold members. The moldmembers themselves may be made thinner or thicker to achieve optimumlens curing results. Different lens curvatures may be made from the samemold members by varying the UV intensity patterns on the mold membersduring cure of the lens forming material. Hardness, cure and rigidity ofthe lenses made as described above may be improved by demolding thelenses and then subjecting the lenses to high intensity UV light and/orheating.

In still another embodiment of the present invention, a photoinitiatoris provided which includes methyl benzoylformate. The photoinitiator maybe used with a composition that includes at least onepolyethylenic-functional monomer containing two ethylenicallyunsaturated groups selected from acrylyl and methacrylyl. Thephotoinitiator may be used with a composition that includes at least onepolyethylenic-functional monomer containing three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl. Thecompositions may include an aromatic containing bis(allylcarbonate)-functional monomer such as bisphenol A his (allyl carbonate).The compositions may include 1,6 hexanediol dimethacrylate,trimethylolpropane triacrylate, tetraethylene glycol diacrylate and/ortripropylene glycol diacrylate. In a preferred embodiment, thecomposition photoinitiator also includes 1-hydroxycyclohexyl phenylketone.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description as well as further objects, features andadvantages of the methods, apparatus and compositions of the presentinvention will be more fully appreciated by reference to the followingdetailed description of presently preferred but nonetheless illustrativeembodiments in accordance with the present invention when taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an apparatus for producing a plasticlens according to the present invention;

FIG. 2 is a cross-sectional view of the apparatus of the presentinvention taken along line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view of the apparatus of the presentinvention taken along line 3--3 of FIG. 2;

FIG. 4 is a detail view of a component of the apparatus of the presentinvention;

FIG. 5 is a detail view of a component of the apparatus of the presentinvention;

FIG. 6 is a cross-sectional view of a lens cell for use in the apparatusof the present invention;

FIG. 7 is a perspective view of an apparatus for producing a plasticlens according to the present invention; and

FIG. 8 is a perspective view of an apparatus for producing a plasticlens according to the present invention.

FIG. 9 is a schematic block diagram of an alternate process and systemfor making and postcuring a plastic lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While various aspects of the present invention are hereinafterillustrated and described as being particularly adapted for theproduction of a plastic lens for use in eyeglasses, it is to beunderstood that lenses for other uses can also be produced, such assafety glasses as well as lenses having high quality optical use forinstrument sightings, photography and light filtration.

Therefore, the present invention is not to be limited only to theembodiments illustrated in the drawings, because the drawings are merelyillustrative of the wide variety of specific embodiments of the presentinvention.

Referring now to FIG. 1, a plastic lens curing chamber of the presentinvention is generally indicated by the reference numeral 10. The lenscuring chamber 10 communicates through a plurality of pipes 12 with anair source (not shown), the purpose of which will be discussed below.

As shown in FIG. 2, the plastic lens curing chamber 10 may include anupper lamp chamber 14, an irradiation chamber 16, and a lower lampchamber 18. The upper lamp chamber 14 may be separated from theirradiation chamber 16 by a plate 20. The lower lamp chamber may beseparated from the irradiation chamber 16 by a plate 22. The upper lampchamber 14, the irradiation chamber 16, and the lower lamp chamber 18may be isolated from ambient air by means of upper lamp chamber doors24, irradiation chamber doors 26, and lower lamp chamber doors 28,respectively. While the upper lamp chamber doors 24, the irradiationchamber doors 26 and the lower lamp chamber doors 28 are shown in FIG. 1as including two corresponding door members, those of ordinary skill inthe art will recognize that the doors 24, 26 and 28 may comprise asingle door member. The upper lamp chamber doors 24, the irradiationchamber doors 26 and the lower lamp chamber doors 28 may be slidinglymounted in guides 30. As shown in FIG. 2, vents 32 may communicate withupper lamp chamber 14 and lower lamp chamber 18 by way of correspondingvent chambers 34 and openings 36 disposed in plate 20 and plate 22. Eachvent 32 may be shielded by a vent cover 38.

As shown in FIG. 3, vents 33 may be disposed in the irradiation chamberdoors 26 and communicate with irradiation chamber 16. Each vent 33 maybe shielded by a vent cover 35.

As shown in FIGS. 2 and 3, a plurality of light generating devices orlamps 40 may be disposed within each of upper lamp chamber 14 and lowerlamp chamber 18. Preferably, upper lamp chamber 14 and lower lampchamber 18 each include three lamps 40 that are arranged in a triangularfashion in which the lamps 40 in the upper lamp chamber 14 are disposedwith the point of the triangle pointing upwards whereas the lamps 40 inthe lower lamp chamber 18 are disposed with the point of the trianglepointing downward. The lamps 40, preferably, generate ultraviolet lighthaving a wavelength in the range of approximately 300 nm to 400 nm sincethe effective wavelength spectrum for curing the lens forming materiallies in the 300 nm to 400 nm region. The lamps 40 may be supported byand electrically connected to suitable fixtures 42.

An exhaust fan 44 may communicate with upper lamp chamber 14 while anexhaust fan 46 may communicate with lower lamp chamber 18.

As noted above, the upper lamp chamber 14 may be separated from theirradiation chamber 16 by plate 20. Similarly, lower lamp chamber 18 maybe separated from the irradiation chamber 16 by plate 22. The plates 20and 22 may include apertures 48 and 50, respectively through which thelight generated by lamps 40 may be directed so as to impinge upon a lenscell 52 (shown in phantom in FIG. 2). The diameter of the lens cell 52according to the present invention, preferably, is approximately 74 mm.The apertures 48 and 50 preferably range from about 70 mm to about 140mm. An upper light filter 54 rests upon plate 20 while a lower lightfilter 56 rests upon plate 22 or is supported by brackets 57. The upperlight filter 54 and lower light filter 56 are shown in FIG. 2 as beingcomprised of a single filter member, however, those of ordinary skill inthe art will recognize that each of the upper light filter 54 and lowerlight filter 56 may be comprised of two filter members. The componentsof upper light filter 54 and lower light filter 56 preferably aremodified depending upon the characteristics of the lens to be molded.For instance, in a preferred embodiment for making negative lenses, theupper light filter 54 includes a plate of Pyrex glass that is frosted onboth sides resting upon a plate of clear Pyrex glass. The lower lightfilter 56 includes a plate of Pyrex glass frosted on one side restingupon a plate of clear Pyrex glass with a device for reducing theintensity of ultraviolet light incident upon the center portion inrelation to the edge portion of the lens being disposed between theplate of frosted Pyrex and the plate of clear Pyrex glass.

Conversely, in a preferred arrangement for producing positive lenses,the upper light filter 54 includes a plate of Pyrex glass frosted on oneor both sides and a plate of clear Pyrex glass resting upon the plate offrosted Pyrex glass with a device for reducing the intensity ofultraviolet light incident upon the edge portion in relation to thecenter portion of the lens being disposed between the plate of clearPyrex glass and the plate of frosted Pyrex glass. The lower light filter56 includes a plate of clear Pyrex glass frosted on one side restingupon a plate of clear Pyrex glass with a device for reducing theintensity of ultraviolet light incident upon the edge portion inrelation to the center portion of the lens being disposed between theplates of clear Pyrex glass. In this arrangement, in place of a devicefor reducing the relative intensity of ultraviolet light incident uponthe edge portion of the lens, the diameter of the aperture 50 can bereduced to achieve the same result, i.e. to reduce the relativeintensity of ultraviolet light incident upon the edge portion of thelens.

It will be apparent to those skilled in the art that each filter 54 or56 could comprise a plurality of filter members or comprise any othermeans or device effective to reduce the light to its desired intensity,to diffuse the light and/or to create a light intensity gradient acrossthe lens cell 52.

Preferably, the upper light filter 54 or the lower light filter 56 eachcomprise at least one plate of Pyrex glass having at least one frostedsurface. Also, either or both of the upper light filter 54 and the lowerlight filter 56 may include more than one plate of Pyrex glass eachfrosted on one or both surfaces, and/or one or more sheets of tracingpaper. After passing through frosted Pyrex glass, the ultraviolet lightis believed to have no sharp intensity discontinuities which is believedto lead to a reduction in optical distortions in the finished lens.Those of ordinary skill in the art will recognize that other means maybe used to diffuse the ultraviolet light so that it has no sharpintensity discontinuities.

Disposed within the irradiation chamber 16 are a left stage 58, a centerstage 60, and a right stage 62, each of which includes a plurality ofsteps 64. The left stage 58 and center stage 60 define a leftirradiation chamber 66 while the right stage 62 and center stage 60define a right irradiation chamber 68. A cell holder 70, shown inphantom in FIG. 2 and in detail in FIG. 4, may be disposed within eachof left irradiation chamber 66 and right irradiation chamber 68. Thecell holder 70 includes a peripheral step 72 that is designed to allow acell holder 70 to be supported upon complementary steps 64 of left stage58 and center stage 60, and center stage 60 and right stage 62,respectively. As shown in FIG. 4, each cell holder 70 also includes acentral bore 74 to allow the passage therethrough of ultraviolet lightfrom the lamps 40 and an annular step 76 which is designed to support alens cell 52 in a manner described below.

As shown in FIG. 6, each lens cell 52 includes opposed mold members 78,separated by an annular gasket 80 to define a lens molding cavity 82.The opposed mold members 78 and the annular gasket 80 may be selected ina manner to produce a lens having a desired diopter.

The mold members 78, preferably, are formed of any suitable materialthat will permit rays of ultraviolet light to pass therethrough. Themold members 78, preferably, are formed of glass. Each mold member 78has an outer peripheral surface 84 and a pair of opposed surfaces 86 and88 with the surfaces 86 and 88 being precision ground. Preferably themold members 78 have desirable ultraviolet light transmissioncharacteristics and both the casting surface 86 and non-casting surface88 preferably have no surface aberrations, waves, scratches or otherdefects as these may be reproduced in the finished lens.

As noted above, the mold members 78 are adapted to be held in spacedapart relation to define a lens molding cavity 82 between the facingsurfaces 86 thereof. The mold members 78 are held in a spaced apartrelation by a T-shaped flexible annular gasket 80 that seals the lensmolding cavity 82 from the exterior of the mold members 78. In use, thegasket 80 is supported on the annular step 76 of the cell holder 70.

In this manner, in the embodiment of the present invention that isillustrated in FIG. 6 the upper or back mold member 90 has a convexinner surface 86 while the lower or front mold member 92 has a concaveinner surface 86 so that the resulting lens molding cavity 82 is shapedto form a lens with a desired configuration. Thus, by selecting the moldmembers 78 with a desired surface 86, lenses with differentcharacteristics, such as focal lengths, may be made by the apparatus 10.Such techniques are well known to those skilled in the art, and willtherefore not be further discussed.

Rays of ultraviolet light emanating from lamps 40 pass through the moldmembers 78 and act on a lens forming material disposed in the moldcavity 82 in a manner discussed below so as to form a lens. As notedabove, the rays of ultraviolet light pass through a suitable filter 54or 56 to impinge upon the lens cell 52.

The mold members 78, preferably, are formed from a material that willnot allow ultraviolet radiation having a wavelength below approximately300 nm to pass therethrough. Suitable materials are Schott Crown, S-1 orS-3 glass manufactured and sold by Schott Optical Glass Inc., of Duryea,Pa. or Corning 8092 glass sold by Corning Glass of Corning, N.Y.

The annular gasket 80 may be formed of vinyl material that exhibits goodlip finish and maintains sufficient flexibility at conditions throughoutthe lens curing process. In a preferred embodiment, the annular gasket80 is formed of silicone rubber material such as GE SE6035 which iscommercially available from General Electric. In another preferredembodiment, the annular gasket 80 is formed of copolymers of ethyleneand vinyl acetate which are commercially available from E. I. DuPont deNemours & Co. under the trade name ELVAX®. Preferred ELVAX® resins areELVAX® 350 having a melt index of 17.3-20.9 dg/min and a vinyl acetatecontent of 24.3-25.7 wt. %, ELVAX® 250 having a melt index of 22.0-28.0dg/min and a vinyl acetate content of 27.2-28.8 wt. %, ELVAX® 240 havinga melt index of 38.0-48.0 dg/min and a vinyl acetate content of27.2-28.8 wt. %, and ELVAX® 150 having a melt index of 38.0-48.0 dg/minand a vinyl acetate content of 32.0-34.0 wt. %. Regardless of theparticular material, the gaskets 80 may be prepared by conventionalinjection molding or compression molding techniques which are well-knownby those of ordinary skill in the art.

As shown in phantom in FIG. 2, in section in FIG. 3, and in detail inFIG. 5, an upper and lower air distribution device 94 is disposed ineach of left irradiation chamber 66 and right irradiation chamber 68.Each air distribution device 94 is connected to a pipe 12. As shown inFIG. 5, each air distribution device 94 includes a plenum portion 95 anda cylindrical opening 96 having orifices 98 disposed therein to allowfor the expulsion of air from the air distribution device 94. Thediameter of the orifices 98 varies around the circumference ofcylindrical opening 96 preferably reaching a maximum when directlyopposite the plenum portion 95 of air distribution device 94 andpreferably reaching a minimum immediately adjacent the plenum portion95. In addition, the orifices 98 are designed to blow air toward a lenscell 52 that may be disposed in a lens cell holder 70 and installed inleft irradiation chamber 66 or right irradiation chamber 68.

In operation, the apparatus of the present invention may beappropriately configured for the production of positive lenses which arerelatively thick at the center or negative lenses which are relativelythick at the edge. To reduce the likelihood of premature release, therelatively thick portions of a lens preferably are polymerized at afaster rate than the relatively thin portions of a lens.

The rate of polymerization taking place at various portions of a lensmay be controlled by varying the relative intensity of ultraviolet lightincident upon particular portions of a lens. The rate of polymerizationtaking place at various portions of a lens may also be controlled bydirecting air across the mold members 78 to cool the lens cell 52.

For positive lenses the intensity of incident ultraviolet light,preferably, is reduced at the edge portion of the lens so that thethicker center portion of the lens polymerizes faster than the thinneredge portion of the lens. Conversely, for a negative lens, the intensityof incident ultraviolet light, preferably, is reduced at the centerportion of the lens so that the thicker edge portion of the lenspolymerizes faster than the thinner center portion of the lens. Foreither a positive lens or a negative lens, air may be directed acrossthe faces of the mold members 78 to cool the lens cell 52. As theoverall intensity of incident ultraviolet light is increased, morecooling is needed which can be accomplished by either or both ofincreasing the velocity of the air and reducing the temperature of theair.

It is well known by those of ordinary skill in the art that lens formingmaterials having utility in the present invention tend to shrink as theycure. If the relatively thin portion of a lens is allowed to polymerizebefore the relatively thick portion, the relatively thin portion willtend to be rigid at the time the relatively thick portion cures andshrinks and the lens will either release prematurely from or crack themold members 78. Accordingly, when the relative intensity of ultravioletlight incident upon the edge portion of a positive lens is reducedrelative to the center portion, the center portion polymerizes fasterand shrinks before the edge portion is rigid so that the shrinkage ismore uniform. Conversely, when the relative intensity of ultravioletlight incident upon the center portion of a negative lens is reducedrelative to the edge portion, the edge portion polymerizes faster andshrinks before the center becomes rigid so that the shrinkage is moreuniform.

According to the present invention, the variation of the relativeintensity of ultraviolet light incident upon a lens may be accomplishedin a variety of ways. According to one method, in the case of a positivelens,.a ring of opaque material may be placed between the lamps 40 andthe lens cell 52 so that the incident ultraviolet light falls mainly onthe thicker center portion of the lens. Conversely, for a negative lens,a disk of opaque material may be placed between the lamps 40 and thelens cell 52 so that the incident ultraviolet light falls mainly on theedge portion of the lens.

According to another method, in the case of a negative lens, a sheetmaterial having a variable degree of opacity ranging from opaque at acentral portion to transparent at a radial outer portion is disposedbetween the lamps 40 and the lens cell 52. Conversely, for a positivelens, a sheet material having a variable degree of opacity ranging fromtransparent at a central portion to opaque at a radial outer portion isdisposed between the lamps 40 and the lens cell 52.

According to still another method, a plurality of ultraviolet-lightabsorbing geometric or random shapes are printed and arranged on a sheetmaterial. In the case of a positive lens, the density of the shapes isgreatest at a radial outer portion while the density of the shapes issmallest at a central portion of the pattern. Conversely, in the case ofa negative lens, the density of the shapes is smallest at a radial outerportion while the density of the shapes is greatest at a central portionof the pattern.

Those of ordinary skill in the art will recognize that there are a widevariety of techniques other than those enumerated above for varying theintensity of the ultraviolet light incident upon the opposed moldmembers 78.

The intensity of the incident light has been measured and determined tobe approximately 3.0 to 5.0 milliwatts per square centimeter (mW/cm²)prior to passing through either the upper light filter 54 or the lowerlight filter 56 and the total intensity at the thickest part of the lensranges from 0.6 to 2.0 mW/cm² while the intensity at the thinnestportion of the lens ranges from 0.1 to 1.5 mW/cm². It has also beendetermined that the overall light intensity incident on the lens cell 52has less of an impact on the final product than the relative lightintensity incident upon the thick or thin portions of the lens so longas the lens cell 52 is sufficiently cooled to reduce the polymerizationrate to an acceptable level.

According to the present invention, it has been determined that thefinished power of an ultraviolet light polymerized lens may becontrolled by manipulating the distribution of the incident ultravioletlight striking the opposed mold members 78. For instance, for anidentical combination of mold members 78 and gasket 80, the focusingpower of the produced lens may be increased or decreased by changing thepattern of intensity of ultraviolet light across the lens mold cavity 82or the faces of the opposed mold members 78.

As the lens forming material begins to cure, it passes through a gelstate, the pattern of which within the lens cell 52 leads to the properdistribution of internal stresses generated later in the cure when thelens forming material begins to shrink.

As the lens forming material shrinks during the cure, the opposed moldmembers 78 will flex as a result of the different amounts of shrinkagebetween the relatively thick and the relatively thin portions of thelens. When a negative lens, for example, is cured, the upper or backmold member 90 will flatten and the lower or front mold member 92 willsteepen with most of the flexing occurring in the lower or front moldmember 92. Conversely, with a positive lens, the upper or back moldmember 90 will steepen and the lower or front mold member 92 willflatten with most of the flexing occurring in the upper or back moldmember 90.

By varying the intensity of the ultraviolet light between the relativelythin and the relatively thick portions of the lens in the lens formingcavity 82, it is possible to create more or less total flexing. Thoselight conditions which result in less flexing will minimize thepossibility of premature release.

The initial curvature of the opposed mold members 78 and the centerthickness of the lens produced can be used to compute the theoretical orpredicted power of the lens. The ultraviolet light conditions can bemanipulated to alter the power of the lens to be more or less thanpredicted. For example, when a disk of opaque material is positionedbetween the lower lamp chamber 18 and the lens cell 52, less totalflexure is observed. The greater the diameter of the disk of opaquematerial, the more negative (-) power the resultant lens will exhibit.

When the lenses cured by the ultraviolet light are removed from theopposed mold members 78, they are under a stressed condition. It hasbeen determined that the power of the lens can be brought to a finalresting power, by subjecting the lenses to a post-curing heat treatmentto relieve the internal stresses developed during the cure and cause thecurvature of the front and the back of the lens to shift. Typically, thelenses are cured by the ultraviolet light in about 10-30 minutes(preferably about 15 minutes). The post-curing heat treatment isconducted at approximately 85°-120° C. for approximately 5-15 minutes.Preferably, the post-curing heat treatment is conducted at 100°-110° C.for approximately 10 minutes. Prior to the post-cure, the lensesgenerally have a lower power than the final resting power. Thepost-curing heat treatment reduces yellowing of the lens and reducesstress in the lens to alter the power thereof to a final power. Thepost-curing heat treatment can be conducted in a conventional convectionoven or any other suitable device.

According to the present invention, the ultraviolet lamps 40 preferablyare maintained at a temperature at which the lamps 40 deliver maximumoutput. The lamps 40, preferably, are cooled because the intensity ofthe light produced by the lamps 40 fluctuates when the lamps 40 areallowed to overheat. In the apparatus of the present invention depictedin FIG. 2, the cooling of the lamps 40 is accomplished by suckingambient air into the upper lamp chamber 14 and lower lamp chamber 18through vent 32, vent chambers 34 and openings 36 by means of exhaustfans 44 and 46, respectively. Excessive cooling of the lamps 40 shouldbe avoided, however, as the intensity of the light produced by the lamps40 is reduced when the lamps 40 are cooled to an excessive degree.

As noted above, according to the present invention, the lens cell 52,preferably, is cooled during curing of the lens forming material as theoverall intensity of the incident ultraviolet light is increased.Cooling of the lens cell 52 generally reduces the likelihood ofpremature release by slowing the reaction and improving adhesion. Thereare also improvements in the optical quality, stress characteristics andimpact resistance of the lens. Cooling of the lens cell 52, preferably,is accomplished by blowing air across the lens cell 52. The airpreferably has a temperature ranging between 15° and 85° F. (about -9.4°C. to 29.4° C.) to allow for a curing time of between 30 and 10 minutes.The air distribution device 94 depicted in FIG. 5 have been found to beparticularly advantageous as they are specifically designed to directair directly across the surface of the opposed mold members 78. Afterpassing across the surface of the opposed mold members 78, the airemanating from the air distribution devices 94 is vented through vents33. Alternately the air emanating from the air distribution devices 94may be recycled back to an air cooler 312, such as is shown in FIG. 9.

The lens cell 52 may also be cooled by disposing the lens cell in aliquid cooling bath.

The opposed mold members 78, preferably, are thoroughly cleaned betweeneach curing run as any dirt or other impurity on the mold members 78 maycause premature release. The mold members 78 are cleaned by anyconventional means well known to those of ordinary skill in the art suchas with a domestic cleaning product i.e. Mr. Clean® available fromProcter and Gamble. Those of ordinary skill in the art will recognize,however, that many other techniques may also be used for cleaning themold members 78.

Yellowing of the finished lens may be related to the monomercomposition, the identity of the photoinitiator and the concentration ofthe photoinitiator.

When casting a lens, particularly a positive lens that is thick in thecenter, cracking may be a problem. Addition polymerization reactions,including photochemical addition polymerization reactions, areexothermic. During the process, a large temperature gradient may buildup and the resulting stress may cause the lens to crack.

When the polymerization reaction proceeds too rapidly, heat buildupinside the system which leads to cracking is inevitable. The likelihoodof cracking increases as the temperature difference between the centerof the lens forming material and room temperature increases. During thepolymerization process, several forces tending to crack the lens, suchas shrinkage, adhesion, and thermal gradients, are at work. Other forcestending to crack the lens may occur when the irradiation is stopped andthe lens is cooled, especially if the lens cell 52 is allowed to cooltoo quickly.

The formation of optical distortions usually occurs during the earlystages of the polymerization reaction during the transformation of thelens forming composition from the liquid to the gel state. Once patternsleading to optical distortions form they are difficult to eliminate.When gelation occurs there is a rapid temperature rise. The exothermicpolymerization step causes a temperature increase, which in turn causesan increase in the rate of polymerization, which causes a furtherincrease in temperature. If the heat exchange with the surroundings isnot sufficient enough there will be a runaway situation that leads topremature release, the appearance of thermally caused striations andeven breakage. Since the rate of polymerization increases rapidly at thegelation point, this is an important phase of the reaction.

Accordingly, it is preferred that the reaction process be smooth and nottoo fast but not too slow. Heat is preferably not generated by theprocess so fast that it cannot be exchanged with the surroundings. Theincident ultraviolet light intensity preferably is adjusted to allow thereaction to proceed at a desired rate. It is also preferred that theseal between the annular gasket 80 and the opposed mold members 78 is ascomplete as possible.

Factors that have been found to lead to the production of lenses thatare free from optical distortions are (1) achieving a good seal betweenthe annular gasket 80 and the opposed mold members 78; (2) using moldmembers 78 having surfaces that are free from defects; (3) using aformulation having an appropriate type and concentration ofphotoinitiator that will produce a reasonable rate of temperature rise;and (4) using a homogeneous formulation. Preferably, these conditionsare optimized.

Premature release of the lens from the mold will result in anincompletely cured lens and the production of lens defects. Factors thatcontribute to premature release are (1) a poorly assembled lens cell 52;(2) the presence of air bubbles around the sample edges; (3)imperfection in gasket lip or mold edge; (4) inappropriate formulation;(5) uncontrolled temperature rise; and (6) high or nonuniform shrinkage.Preferably, these conditions are minimized.

Premature release may also occur when the opposed mold members 78 areheld too rigidly by the annular gasket 80. Preferably, there issufficient flexibility in the annular gasket 80 to permit the opposedmold members 78 to follow the lens as it shrinks. Indeed, the lens mustbe allowed to shrink in diameter slightly as well as in thickness. Theuse of an annular gasket 80 that has a reduced degree of stickiness withthe lens during and after curing is therefore desirable.

In a preferred technique for filling the lens molding cavity 82, theannular gasket 80 is placed on a concave or front mold member 92 and aconvex or back mold member 90 is moved into place. The annular gasket 80is then pulled away from the edge of the back mold member 90 at theuppermost point and a lens forming composition is injected into the lensmolding cavity 82 until a small amount of the lens forming compositionis forced out around the edge. The excess is then removed, preferably,by vacuum. Excess liquid that is not removed could spill over the faceof the back mold member 90 and cause optical distortion in the finishedlens.

Despite the above problems, the advantages offered by the radiationcured lens molding system clearly outweigh the disadvantages. Theadvantages of a radiation cured system include a significant reductionin energy requirements, curing time and other problems normallyassociated with conventional thermal systems.

According to the present invention, the lens forming material cancomprise any suitable liquid monomer or monomer mixture and any suitablephotosensitive initiator. The lens forming material, preferably, doesnot include any component, other than a photoinitiator, that absorbsultraviolet light having a wavelength in the range of 300 to 400 nm. Theliquid lens forming material, preferably, is filtered for qualitycontrol and placed in the lens molding cavity 82 by pulling the annulargasket 80 away from one of the opposed mold members 78 and injecting theliquid lens forming material into the lens molding cavity 82. Once thelens molding cavity 82 is filled with such material, the annular gasket80 is replaced into its sealing relation with the opposed mold members78. The material can then be irradiated with ultraviolet light in themanner described above for a time period that is necessary to cure thelens forming material, preferably approximately 10 to approximately 30minutes. The ultraviolet light entering the lens molding cavity 82preferably has a wavelength in the range of approximately 300 nm. toapproximately 400 nm.

Those skilled in the art will recognize that once the cured lens isremoved from the lens molding cavity 82 by disassembling the opposedmold members 78, the lens can be further processed in a conventionalmanner, such as by grinding its peripheral edge.

According to the present invention a polymerizable lens formingcomposition comprises an aromatic-containing bis(allylcarbonate)-functional monomer and at least one polyethylenic-functionalmonomer containing two ethylenically unsaturated groups selected fromacrylyl and methacrylyl. In a preferred embodiment, the compositionfurther comprises a suitable photoinitiator. In other preferredembodiments, the composition may include one or morepolyethylenic-functional monomers containing three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl, and a dye.

Aromatic-containing bis(allyl carbonate)-functional monomers which canbe utilized in the practice of the present invention are bis(allylcarbonates) of dihydroxy aromatic-containing material. The dihydroxyaromatic-containing material from which the monomer is derived may beone or more dihydroxy aromatic-containing compounds. Preferably thehydroxyl groups are attached directly to nuclear aromatic carbon atomsof the dihydroxy aromatic-containing compounds. The monomers arethemselves known and can be prepared by procedures well known in theart.

The aromatic-containing bis(allyl carbonate )-functional monomers can berepresented by the formula: ##STR1##

in which A₁ is the divalent radical derived from the dihydroxyaromatic-containing material and each R₀ is independently hydrogen,halo, or a C₁ -C₄ alkyl group. The alkyl group is usually methyl orethyl. Examples of R₀ include hydrogen, chloro, bromo, fluoro, methyl,ethyl, n-propyl, isopropyl and n-butyl. Most commonly R₀ is hydrogen ormethyl; hydrogen is preferred. A subclass of the divalent radical A₁which is of particular usefulness is represented by the formula:##STR2##

in which each R₁ is independently alkyl containing from 1 to about 4carbon atoms, phenyl, or halo; the average value of each a isindependently in the range of from 0 to 4; each Q is independently oxy,sulfonyl, alkanediyl having from 2 to about 4 carbon atoms, oralkylidene having from 1 to about 4 carbon atoms; and the average valueof n is in the range of from 0 to about 3. Preferably Q ismethylethylidene, viz., isopropylidene.

Preferably the value of n is zero, in which case A₁ is represented bythe formula: ##STR3##

in which each R₁, each a, and Q are as discussed in respect of FormulaII. Preferably the two free bonds are both in the ortho or parapositions. The para positions are especially preferred.

The dihydroxy aromatic-containing compounds from which A₁ is derived mayalso be polyol-functional chain extended compounds. Examples of suchcompounds include alkaline oxide extended bisphenols. Typically thealkaline oxide employed is ethylene oxide, propylene oxide, or mixturesthereof. By way of exemplification, when para, para-bisphenols are chainextended with ethylene oxide, the bivalent radical A₁ may often berepresented by the formula: ##STR4## where each R₁, each a, and Q are asdiscussed in respect of Formula II, and the average values of j and kare each independently in the range of from about 1 to about 4.

The preferred aromatic-containing bis(allyl carbonate)-functionalmonomer is represented by the formula: ##STR5##

and is commonly known as bisphenol A bis(allyl carbonate).

A wide variety of compounds may be used as the polyethylenic functionalmonomer containing two or three ethylenically unsaturated groups. Thepreferred polyethylenic functional compounds containing two or threeethylenically unsaturated groups may be generally described as theacrylic acid esters and the methacrylic acid esters of aliphaticpolyhydric alcohols, such as, for example, the di- and triacrylates andthe di- and trimethacrylates of ethylene glycol, triethylene glycol,tetraethylene glycol, tetramethylene glycol, glycidyl, diethyleneglycol,butyleneglycol, propyleneglycol, pentanediol, hexanediol,trimethylolpropane, and tripropyleneglycol. Examples of specificsuitable polyethylenic-functional monomers containing two or threeethylenically unsaturated groups include trimethylolpropanetriacrylate(TMPTA), tetraethylene glycol diacrylate (TTEGDA), tripropylene glycoldiacrylate (TRPGDA), 1,6 hexanedioldimethacrylate (HDDMA), andhexanedioldiacrylate (HDDA).

In general, a photoinitiator for initiating the polymerization of thelens forming composition of the present invention, preferably, exhibitsan ultraviolet absorption spectrum over the 300-400 nm range. Highabsorptivity of a photoinitiator in this range, however, is notdesirable, especially when casting a thick lens. The following areexamples of illustrative photoinitiator compounds within the scope ofthe invention: methyl benzoylformate,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenylketone, 2,2-di-sec-butoxyacetophenone, 2,2-diethoxyacetophenone,2,2-diethoxy-2-phenyl-acetophenone, 2,2-dimethoxy-2-phenyl-acetophenone,benzoin methyl ether, benzoin isobutyl ether, benzoin, benzil, benzyldisulfide, 2,4-dihydroxybenzophenone, benzylideneacetophenone,benzophenone and acetophenone. Preferred photoinitiator compounds are1-hydroxycyclohexyl phenyl ketone (which is commercially available fromCiba-Geigy as Irgacure 184), methyl benzoylformate (which iscommercially available from Polysciences, Inc.), or mixtures thereof.

Methyl benzoylformate is a generally preferred photoinitiator because ittends to provide a slower rate of polymerization. The slower rate ofpolymerization tends to prevent excessive heat buildup (and resultantcracking of the lens) during polymerization. In addition, it isrelatively easy to mix liquid methyl benzoylformate (which is liquid atambient temperatures) with many acrylates, diacrylates, and allylcarbonate compounds to form a lens forming composition. The lensesproduced with the methyl benzoylformate photoinitiator tend to exhibitmore favorable stress patterns and uniformity.

A strongly absorbing photoinitiator will absorb most of the incidentlight in the first millimeter of lens thickness, causing rapidpolymerization in that region. The remaining light will produce a muchlower rate of polymerization below this depth and will result in a lensthat has visible distortions. An ideal photoinitiator will exhibit highactivity, but will have a lower extinction coefficient in the usefulrange. A lower extinction coefficient of photoinitiators at longerwavelengths tends to allow the ultraviolet radiation to penetrate deeperinto the reaction system. This deeper penetration of the ultravioletradiation allows photoinitiator radicals to form uniformly throughoutthe sample and provide excellent overall cure. Since the sample can beirradiated from both top and bottom, a system in which appreciable lightreaches the center of the thickest portion of the lens is preferred. Thephotoinitiator solubility and compatibility with the monomer system isalso an important requirement.

An additional consideration is the effect of the photoinitiatorfragments in the finished polymer. Some photoinitiators generatefragments that impart a yellow color to the finished lens. Although suchlenses actually absorb very little visible light, they are cosmeticallyundesirable.

Photoinitiators are often very system specific so that photoinitiatorsthat are efficient in one system may function poorly in another. Inaddition, the initiator concentration to a large extent is dependent onthe incident light intensity and the monomer composition. The identityof the initiator and its concentration are important for any particularformulation. A concentration of initiator that is too high tends to leadto cracking and yellowing of the lens. Concentrations of initiator thatare too low tend to lead to incomplete polymerization and a softmaterial.

Dyes and/or pigments are optional materials that may be present whenhigh transmission of light is not necessary.

The listing of optional ingredients discussed above is by no meansexhaustive. These and other ingredients may be employed in theircustomary amounts for their customary purposes so long as they do notseriously interfere with good polymer formulating practice.

According to a preferred embodiment of the present invention, thepreferred aromatic-containing bis(allyl carbonate) functional monomer,bisphenol A bis(allyl carbonate) is admixed with one or more fasterreacting polyethylenic functional monomers containing two acrylate ormethacrylate groups such as 1,6 hexanediol dimethacrylate (HDDMA), 1,6hexanediol diacrylate (HDDA), tetraethylene glycol diacrylate (TTEGDA),and tripropylene glycol diacrylate (TRPGDA) and optionally apolyethylenic functional monomer containing three acrylate groups suchas trimethylolpropane triacrylate (TMPTA). Generally, compoundscontaining acrylate groups polymerize much faster than those containingallyl groups.

The lamps 40 generate an intensity at the lamp surface of approximately4.0 to 7.0 mW/cm² of ultraviolet light having wavelengths between 300and 400 nm, which light is very uniformly distributed without any sharpdiscontinuities throughout the reaction process. Such bulbs arecommercially available from Sylvania under the trade designationSylvania Fluorescent (F158T/2052) or Sylvania Fluorescent(F258T8/350BL/18") GTE. As noted above, ultraviolet light havingwavelengths between 300 and 400 nm is preferred because thephotoinitiators according to the present invention, preferably, absorbmost efficiently at this wavelength and the mold members 78, preferably,allow maximum transmission at this wavelength.

It is preferred that there be no sharp intensity gradients ofultraviolet radiation either horizontally or vertically through the lenscomposition during the curing process. Sharp intensity gradients throughthe lens may lead to defects in the finished lens.

According to one embodiment of the present invention, the liquid lensforming composition includes bisphenol A bis(allyl carbonate) in placeof DEG-BAC. The bisphenol A bis(allyl-carbonate) monomer has a higherrefractive index than DEG-BAC which allows the production of thinnerlenses which is important with relatively thick positive or negativelenses. The bisphenol A bis(allyl-carbonate) monomer is commerciallyavailable from PPG Industries under the trade name HIRI I or CR-73.Lenses made from this product sometimes have a very slight, barelydetectable, degree of yellowing. A small amount of a blue dye consistingof 9,10-anthracenedione, 1-hydroxy-4-[(4-methylphenyl)amino] availableas Thermoplast Blue 684 from BASF Wyandotte Corp. is preferably added tothe composition to counteract the yellowing. In addition, the yellowingtends to disappear if the lens is subjected to the above-describedpost-cure heat treatment. Moreover, if not post-cured the yellowingtends to disappear at ambient temperature after approximately 2 months.

According to a preferred embodiment, the composition of the presentinvention includes (a) bisphenol A-bis(allyl carbonate); (b) at leastone of HDDMA, TTEGDA and TRPGDA; and (c) a photoinitiator. According tothis embodiment the composition may also include one or both of TMPTAand a dye.

According to another preferred embodiment, the composition of thepresent invention includes (a) up to 70 percent by weight of bisphenol Abis(allyl carbonate); (b) up to 100 percent by weight of HDDMA; (c) upto 100 percent by weight of TTEGDA; (d) up to 100 percent by weight ofTRPGDA; and (e) up to 100 percent by weight of TMPTA. Preferably, thecomposition further comprises (f) up to about 1.0 percent by weight of1-hydroxycyclohexylphenyl ketone; and (g) up to about 1.2 percent byweight of methyl benzoylformate. Preferably the composition furthercomprises (h) up to about 1.0 parts per million (ppm) of9,10-anthracenedione, 1-hydroxy-4-[(4-methylphenyl)amino].

According to still another preferred embodiment, the composition of thepresent invention includes (a) about 15.0 to about 25.0 percent byweight of bisphenol A bis(allyl-carbonate); (b) about 8.0 to about 14.0percent by weight of HDDMA; (c) about 15.0 to about 25.0 percent byweight of TTEGDA; (d) about 17.0 to about 37.0 percent by weight ofTRPGDA; and (e) about 15.0 to about 25.0 percent by weight of TMPTA. Thecomposition may also include (f) about 0.003 to about 0.04 percent byweight of 1-hydroxycyclohexylphenyl ketone, (g) about 0.015 to about0.05 percent by weight of methyl benzoylformate, and (h) about 0.16 toabout 0.20 ppm of 9,10-anthracenedione,1-hydroxy-4-[(4-methylphenyl)amino].

According to a further preferred embodiment, the composition includes17.0% by weight of bisphenol A bis(allyl carbonate), 10.0% by weight ofHDDMA, 21.0% by weight of TTEGDA, 32.0% by weight of TRPGDA, and 20.0%by weight of TMPTA. The composition may also include 0.0095% by weightof 1-hydroxycyclohexylphenyl ketone, 0.0356% by weight of methylbenzoylformate, and 0.16 ppm of 9,10-anthracenedione,1-hydroxy-4-[(4-methylphenyl)amino].

As discussed above, bisphenol A bis(allyl carbonate) has a higherrefractive index than DEG-BAC and thus allows the production of thinnerlenses when compared to DEG-BAC lenses.

TTEGDA, available from Sartomer and Radcure, is a diacrylate monomerthat, preferably, is included in the composition because it is a fastpolymerizing monomer that reduces yellowing and yields a very clearproduct. If too much TTEGDA is included in the most preferredcomposition, i.e. greater than about 25% by weight, however, thefinished lens may be prone to cracking and may be too flexible as thismaterial softens at temperatures above 40° C. If TTEGDA is excludedaltogether, the finished lens may to be brittle.

HDDMA, available from Sartomer, is a dimethacrylate monomer that has avery stiff backbone between the two methacrylate groups. HDDMA,preferably, is included in the composition because it yields a stifferpolymer and increases the hardness and strength of the finished lens.This material is quite compatible with the bisphenol A bis(allylcarbonate) monomer. HDDMA contributes to high temperature stiffness,polymer clarity and speed of polymerization.

TRPGDA, available from Sartomer and Radcure, is a diacrylate monomerthat, preferably, is included in the composition because it providesgood strength and hardness without adding brittleness to the finishedlens. This material is also stiffer than TTEGDA.

TMPTA, available from Sartomer and Radcure, is a triacrylate monomerthat, preferably, is included in the composition because it providesmore crosslinking in the finished lens than the difunctional monomers.TMPTA has a shorter backbone than TTEGDA and increases the hightemperature stiffness and hardness of the finished lens. Moreover, thismaterial contributes to the prevention of optical distortions in thefinished lens. TMPTA also contributes to high shrinkage duringpolymerization. The inclusion of too much of this material in the mostpreferred composition may make the finished lens too brittle.

Certain of the monomers that are preferably utilized in the compositionof the present invention, such as TTEGDA, TRPGDA and TMPTA, includeimpurities and have a yellow color in certain of their commerciallyavailable forms. The yellow color of these monomers is preferablyreduced or removed by passing them through a column of alumina (basic)which includes aluminum oxide powder-basic. After passage through thealumina column, the monomers absorb almost no ultraviolet light. Alsoafter passage through the alumina column differences between monomersobtained from different sources are substantially eliminated. It ispreferred, however, that the monomers be obtained from a source whichprovides the monomers with the least amount of impurities containedtherein. The composition preferably is filtered prior to polymerizationthereof to remove suspended particles.

The composition of the present invention, preferably, may be preparedaccording to the following protocol. Appropriate amounts of HDDMA,TTEGDA, TMPTA and TRPGDA are mixed and stirred thoroughly, preferablywith a glass rod. The acrylate/methacrylate mixture may then be passedthrough a purification column.

A suitable purification column may be disposed within a glass columnhaving a fitted glass disk above a teflon stopcock and having a topreservoir with a capacity of approximately 500 ml and a body with adiameter of 22 mm and a length of about 47 cm. The column may beprepared by placing on the fitted glass disk approximately 35 g. ofactivated alumina (basic), available from ALFA Products, JohnsonMatthey, Danvers, Mass. in a 60 mesh form or from Aldrich in a 150 meshform. Approximately 10 g. of an inhibitor remover(hydroquinone/methylester remover) available as HR-4 from ScientificPolymer Products, Inc., Ontario, N.Y. then may be placed on top of thealumina and, finally, approximately 35 g. of activated alumina (basic)may be placed on top of the inhibitor remover.

Approximately 600 g. of the acrylate/methacrylate mixture may then beadded above the column packing. An overpressure of 2-3 psi may then beapplied to the top of the column resulting in a flow rate ofapproximately 30 to 38 grams per hour. Parafilm may be used to cover thejunction of the column tip and the receiving bottle to prevent theinfiltration of dust and water vapor. The acrylate/methacrylate mixture,preferably, may be received in a container that is opaque to ultravioletradiation.

An appropriate amount of bisphenol A bis(allyl carbonate) may then beadded to the acrylate/methacrylate mixture to prepare the final monomermixture.

An appropriate amount of a photoinitiator may then be added to the finalmonomer mixture. The final monomer mixture, with or withoutphotoinitiator, may then be stored in a container that is opaque toultraviolet radiation.

An appropriate amount of a dye may also be added to the final monomermixture, with or without photoinitiator.

After edging, the ultraviolet light cured lenses of the presentinvention demonstrate excellent organic solvent resistance to acetone,methylethyl ketone, and alcohols.

Premature release may occur if the temperature rise of the lens formingcomposition is uncontrolled. Premature release may also occur if theopposed mold members 78 are held too rigidly by the annular gasket 80.There is preferably sufficient flexibility in the gaskets 80 to permitthe mold members 78 to follow the lens as it shrinks. Insufficientsealing, unsuitable gasket material and/or a small residual amount ofuncured material have also been found to contribute to premature releasefailures.

For best results, both the casting surfaces 86 and non-casting surfaces88 of the mold members 78 are finished to optical quality. For instance,a wave on the non-casting surface 88 may be reproduced in the finishedlens as a result of the distortion of the incident light.

Mold markings cause differential light intensity conditions under themarking, even when the mark is on the non-casting surface 88 of the moldmembers 78. The fully exposed region of the lens will tend to be harder,and the lens may have stresses because of this. The portion of the lensunder the mark will also tend to be weaker at the end of the curingperiod. This effect has been observed and may cause premature release orinduce cracking.

Mold defects at the edges interfere with the sealing conditions andfrequently induce premature release.

According to the present invention, plastic lenses may be produced byirradiating the lens forming material with ultraviolet light that isprevented from passing through the faces of the opposed mold members 78and instead passes through the transparent or translucent wall ofannular gasket 80 of the lens cell 52. By irradiating in this manner,the thicker edge portion of a negative lens receives a higher level oflight intensity than the thinner center portion since the lightintensity drops as it passes through the deeper layers of the lensmaterial and glass molds. This method has a desirable advantage ofallowing the application of clamping pressure to the front and backmolds, which is useful in controlling premature release. This techniquewill be referred to as through-the-gasket irradiation. Referring to FIG.7, apparatus 100 is shown for carrying out through-the-gasketirradiation. Apparatus 100 includes lamp chamber 102 having a pluralityof ultraviolet light generating lamps 104 disposed therein. A lens cell52 in accordance with FIG. 6 is suspended in lamp chamber 102. A cover106 of opaque material is placed over the non-casting surface 88 of eachmold member 78 of the lens cell 52. In this manner, ultraviolet lightemanating from the plurality of lamps 104 that is incident upon the lenscell 52 acts upon the lens forming material disposed in the lens moldingcavity 82 by passing through the outer wall 108 of the annular gasket80. A spring-loaded clamp 110, preferably, may be used to applycompression pressure upon the opposed mold members 78 of the lens cell52. The spring-loaded clamp, preferably, may be adjusted to exertvariable pressure upon the opposed mold members 78. Moreover, opaquedisks 106 may be disposed between the respective jaws of the clamp 110and the mold members 78 to prevent scratching of the molds and toprevent light leakage through the mold.

An alternate technique for through-the-gasket irradiation is shown inFIG. 8. Referring to FIG. 8, apparatus 200 is shown for carrying outthrough-the-gasket irradiation. Apparatus 200 includes opposed lamparrays 202. A lens cell 52 in accordance with FIG. 6 is placed on aturntable 204 disposed between opposed lamp arrays 202. An annularopaque stage 206 is disposed under the front mold member 92 and restsdirectly on turntable 204. A cap 208 of opaque material is disposed onthe back mold member 90. A weight 210 may be disposed upon the back moldmember 90 to exert sufficient clamping pressure to prevent prematurerelease.

According to the through-the-gasket irradiation technique, the annulargaskets 80, preferably, are silicone gaskets. Through continued use,however, silicone gaskets tend to become too opaque to allow sufficientultraviolet light to pass through the gasket to complete thepolymerization of the lens forming material. In addition, gaskets havinga frosty appearance were observed to yield good quality lenses whilegaskets that were clear were observed to yield lenses with opticaldistortions.

The through-the-gasket irradiation techniques make it relatively easy toexert clamping pressure on the mold members 78. Pressure (up to 30 psi)may be applied to the mold members 78, preferably at or about the onsetof gelation of the lens forming material, i.e. after the lens formingmaterial is no longer liquid but before it becomes incompressible. Atthe beginning of the irradiation when the lens forming material isliquid, however, low clamping pressure (such as 2 lb.) may be applied tothe mold members 78, which pressure is not so great that the lensforming material leaks between the gasket 80 and the edges of the moldmembers 78. These techniques also tend to make it easier to directevenly distributed ultraviolet light to the lens forming material. Thegasket 80 serves as a diffuser and prevents sharp intensity gradientsthat occur when light is passing through the mold and there is anirregularity in the mold. Since the edge of a lens receives a higherintensity of ultraviolet light than the center of the lens, thethrough-the-gasket technique, therefore, is quite beneficial for theproduction of negative lenses. Finally, since ultraviolet radiation doesnot pass through the mold members 78 according to this technique, metalmolds which are more flexible (and which tend to exhibit enhanced heattransfer properties) than glass molds can be utilized.

As discussed above, the likelihood of premature release may be affectedby a number of often interrelated factors. Factors such as improper moldcleaning, mold thickness, or gasket/mold design may contribute topremature release. Other factors that may contribute to prematurerelease may include light intensity, the chemical formulations, and theamount and identity of the photoinitiator ("PI"). As discussed above, anadditional factor related to premature release is the exothermic heatgenerated by the reaction.

It is believed that as the reaction proceeds, the heat generated tendsto reduce the adhesion between the shrinking lens and the mold face.This reduction in adhesion tends to cause the lens to pull away from themold. In high curvature (i.e. high power) lenses this problem tends tobe even more pronounced because of two factors: (1) these lenses havemore thickness and thus more material that is generating heat (whichthus speeds up the reaction and generates more heat), and (2) theselenses have a greater thickness differential between the thick and thinportions of the lens, which tends to cause stress on the molds due todifferential shrinkage. It is also possible that the temperaturesgenerated relatively deep inside a thick lens may cause somevaporization of the monomer. The vaporized monomer may then migrate tothe lens/mold interface, breaking the vacuum between the two.

Because of the problem of premature release, preferably high powerlenses are cured to maintain adhesion to the molds. Preferably the moldsflex and accommodate stress.

Preferably premature release is controlled by controlling the exothermicreaction heat. This heat is preferably controlled by directing coolingfluid such as air at the mold faces. Thus in a preferred embodiment theinvention includes the following steps: (1) placing a polymerizable lensforming material in a mold cavity defined in part between a first moldmember and a second mold member, (2) directing ultraviolet rays towardsat least one of the first or second mold members, and (3) cooling thefirst mold member and the second mold member with a fluid. In apreferred embodiment the ultraviolet rays are directed towards the moldmember(s) while the first and second mold members are cooled. The abovesteps may be carried out with an apparatus for making a plastic lensthat includes: (1) a first mold member, (2) a second mold member spacedapart from the first mold member, the first and second mold membersdefining a mold cavity, (3) an ultraviolet light generator forgenerating and directing ultraviolet light toward at least one of thefirst and second mold members during use, (4) an ultraviolet lightfilter disposed between the ultraviolet light generator and the firstmold member, and between the ultraviolet light generator and the secondmold member, and (5) a distributor for directing cooling fluid to themold members during use.

Preferably both the first and second mold members are "directly" cooledby the fluid. That is, preferably the face of the first mold member andthe face of the second mold member is cooled by directing fluid towardsthe face of both of the mold members. The "face" of the mold members isthe outer mold surface that is not contacting either the gasket or thelens forming materials (see FIG. 6). The fluid may be directed atvarious angles towards the face of the mold members.

Generally less preferred results are achieved if only one (instead ofboth) of the mold members is directly cooled. It is believed thatdirectly cooling only one of the mold members tends to result in lesspreferred lenses because doing so unevenly cools the lens materialduring curing. Thus preferably the first and second mold members areboth substantially evenly exposed to the cooling fluid temperatures andflowrates.

Preferably fluid is directed from the edges of the mold member faces tothe center of the mold member faces. In this manner the fluid thatcontacts the edges of the mold members is approximately the sametemperature at all the edges of the mold members, and approximately thesame at all radii from the center of the mold members (with somevariances due to variances in the cavity thickness at certain radii).Thus substantially the same thicknesses of the lens material aresubjected to fluid that is substantially the same temperature, resultingin a more even cooling of the lens material. Generally less favorableresults are achieved if fluid is simply directed across the mold memberssince the fluid temperature and flow rate at the first edge contacted bythe fluid may be somewhat different than the fluid temperature and flowrate at the second mold member edge. Specifically, if cooling fluid ispassed over the lens forming material in one direction only, the sideopposite the source of fluid tends to remain hotter because the fluidpassing over it has picked up the heat from the first side.

Preferably the fluid is air at a temperature of less than 50° C. Thefluid may be below 0° C., however in a preferred embodiment the fluidwas at a temperature of between 0° C. and less than 20° C., preferablyabout 0°-15° C., more preferably about 0°-10° C., more preferably stillabout 3°-8° C. In one preferred embodiment the fluid temperature wasabout 5° C. As shown in FIG. 9, a lens forming apparatus 300 for makinga plastic lens may include a cooler 312 for supplying cool fluid to theapparatus 300 via conduit 314. The fluid may be supplied to theapparatus 300 and then discharged via conduit 320. The fluid dischargedvia conduit 320 may be vented via conduit 318 or it may alternately berecirculated via conduit 316 to the cooler 312. The cooler 312preferably includes a Neslab CFT-50 water/antifreeze chiller (Newington,N.H., U.S.A.). A Neslab-built blower box designed for a minimumtemperature of 3° C. and 8 cubic feet (about 0.224 cubic meters) perminute of air per air distributor 94 was used with the chiller. Theblower box included a heat exchanger coil through which chilled waterwas circulated, a blower, and a plenum-type arrangement for supplyingair to the conduit 314.

If lenses are produced without any mold cooling, the temperature of themold-lens assembly may rise to above 50° C. Low diopter lenses may beprepared in this fashion, but higher plus or minus diopter lenses mayfail. Certain lenses may be made by controlling (e.g., cooling) thetemperature of the lens material during cure with circulating uncooledfluid (i.e., fluid at ambient temperatures). The ambient fluid in thesesystems is directed towards the mold members in the same manner asdescribed above. Circulating ambient temperature fluid permitsmanufacture of a wider range of prescriptions than manufacture of thelenses without any mold cooling at all. For instance, if the temperatureof the circulating air is held at slightly less than room temperature(about 19° C.), prescriptions from +2 to -3 diopter may be successfullycast. Higher diopters, either + or -, often tend to fail withoutcirculating cooled fluid.

Most polymerization factors are interrelated. The ideal temperature ofpolymerization is related to the diopter and thickness of the lens beingcast. Thermal mass is a factor. Lower temperatures (below about 10° C.)are preferred to cast higher + or - diopter lenses. These lowertemperatures tend to permit an increase in photoinitiator concentration,which in turn may speed up the reaction and lower curing time.

Preventing premature release is also somewhat dependent upon theflowrates of cooling fluid, as well as its temperature. For instance, ifthe temperature of the cooling fluid is decreased it may also bepossible to decrease the flowrate of cooling fluid. Similarly, thedisadvantages of a higher temperature cooling fluid may be somewhatoffset by higher flowrates of cooling fluid.

In one embodiment the air flow rates for a dual distributor system(i.e., an air distributor above and below the lens composition) areabout 1-30 standard cubic feet (about 0.028-0.850 standard cubic meters)per minute per distributor, more preferably about 4-20 cubic feet (about0.113-0.566 standard cubic meters) per minute per distributor, and morepreferably still about 9-15 (about 0.255-0.423 standard cubic meters)cubic feet per minute per distributor. "Standard conditions," as usedherein, means 60° F. (about 15.556° C.) and one atmosphere pressure(about 101.325 kilopascals).

In a preferred embodiment the fluid distributor 94 may include 30substantially evenly spaced orifices 98 disposed to allow fluid to bedirected from the distributor 94 to the mold members. In a preferredembodiment the diameter of fifteen orifices 98 on the one-half of thecylindrical opening 96 closest the plenum portion 95 is about 1/4 inch(about 6.35 mm), and the cumulative volume flowrate of air through suchorifices is estimated to be about 6.10 standard cubic feet (about 0.173standard cubic meters) per minute. In the same embodiment the diameterof fifteen orifices 98 on one-half of the cylindrical opening 96opposite the plenum portion 95 is about 5/16 inch (about 7.94 mm), andthe cumulative volume flowrate of air through such orifices is estimatedto be about 8.30 standard cubic feet (about 0.235 standard cubic:meters) per minute. Thus the total flowrate for one distributor isestimated to be about 14.40 standard cubic feet (about 0.408 standardcubic meters) per minute, and the total flowrate for two distributors isestimated to be about 28.80 standard cubic feet (about 0.816 standardcubic meters) per minute.

In the same embodiment the edge of the orifices 98 in the cylindricalopening 96 are tapered out. In such case the cumulative flowrates forthe 1/4 inch (6.35 mm) orifices 98 is estimated to be about 5.89standard cubic feet (about 0.167 standard cubic meters) per minute, andthe flowrate for the 5/16 inch (7.94 mm) orifices 98 is estimated to beabout 7.02 standard cubic feet (about 0.199 standard cubic meters) perminute. Thus the total flowrate for one distributor is estimated to beabout 12.91 standard cubic feet (about 0.366 standard cubic meters) perminute, and the total flowrate for two distributors is estimated to beabout 25.82 standard cubic feet (about 0.731 standard cubic meters) perminute.

In an alternate preferred embodiment the diameter of fifteen orifices 98on the one-half of the cylindrical opening 96 closest to the plenumportion 95 are about 3/16 inch (about 4.76 mm), and the cumulativevolume flowrate of air through such orifices is estimated to be about3.47 standard cubic feet (about 0.98 standard cubic meters) per minute.In the same embodiment the diameter of fifteen orifices 98 on theone-half of the cylindrical opening 96 opposite the plenum portion 95are about 1/4 inch (about 6.35 mm), and the cumulative volume flowrateof air through such orifices is estimated to be about 6.17 standardcubic feet (about 0.175 standard cubic meters) per minute. Thus thetotal flowrate for one distributor is estimated to be about 9.64standard cubic feet (about 0.273 standard cubic meters) per minute, andthe total flowrate for two distributors is estimated to be about 19.28standard cubic feet (about 0.546 standard cubic meters) per minute.

Actual flowrates through individual orifices 98 tended to vary. Theflowrates through the orifices 98 that were closest to or most oppositethe plenum portion 95 of air distribution device 94 tended to have aflowrate that is greater than orifices in between these orifices. Thesehigher flowrates varied up to approximately 1.2-2.5 times the flowrateof orifices that were in between the closest to and most oppositeorifices.

The above estimated flowrates for orifices 98 in a preferred embodimentwere calculated using a bench model of air distributor 94 connected toair flowrate measuring devices. The air flowrates for the orifices 98 inthe bench model were measured. The total air flowrate through the benchmodel distributor 94 was measured. The total air flowrate for apreferred embodiment distributor 94 was measured. The above flowrateswere measured by measuring the average velocity across a cross-sectionalarea, and then multiplying such velocity by the cross-sectional area.The estimated flowrates for the preferred embodiment orifices 98 wereobtained by the following equation:

    P.sub.o =B.sub.o ×(P.sub.A /B.sub.A),

where

P_(o) =estimated preferred embodiment orifices 98 flowrate,

P_(A) =measured preferred embodiment distributor 94 flowrate,

B_(o) =measured bench orifices 98 flowrate, and

B_(A) =measured bench distributor 94 flowrate.

The thickness of the glass molds used to cast polymerized lenses mayaffect the lenses produced. A thinner mold tends to allow more efficientheat transfer between the polymerizing material and the cooling air,thus reducing the rate of premature release. In addition, a thinner moldtends to exhibit a greater propensity to flex. A thinner mold tends toflex during the relatively rapid differential shrinkage between thethick and thin portions of a polymerized lens, again reducing theincidence of premature release. In one embodiment the first or secondmold members have a thickness less than about 5.0 mm, preferably about1.0-5.0 mm, more preferably about 2.0-4.0 mm, and more still about2.5-3.5 mm.

Higher diopter ("D") lenses both have more mass (and so release moreheat during the curing cycle) and also define a greater differencebetween their thick and thin portions than a lower diopter lens.Accordingly, for 74 mm diameter negative lenses stronger than about-2.00 D, it is preferably to reduce the thickness of the front (concave)mold to less than 4 mm and preferably to between 3.0 to 3.5 mm. CorningGlass #9092 mold material tends to exhibit about 50% greater meandeflection value at 3 mm than at 5 mm.

Because a negative lens is thin in the center and thick at the edge,more shrinkage tends to occur at the edge than at the center. Because ahemispherical section of glass will bend more readily toward its radiusthan away from it, in the case of a minus lens the front mold tends toaccommodate the greater shrinkage at the edge by flexing and steepening.A positive lens is just the opposite. The thick section of a plus lensis its center and the edge is thin. The greater shrinkage of the centertends to cause the back (convex) mold to steepen and the front mold toflex very little. In this situation it is preferable to reduce thethickness of the back molds used to cast high diopter positive lenses soas to help reduce the polymerization strain.

The advantages of using a thinner mold are offset somewhat by twodisadvantages. Using a thinner mold of the exact radius of curvature asa thicker mold will shift the final focusing power of the finished lenstoward the plus side and therefore its radius must be compensatedaccordingly. Further, thicker molds tend to give better overall opticsand show less distortion than the same lens cast with a thin mold.

Preferred mold thicknesses for lenses with a diameter of about 74 mmvary depending on the diopter of the lenses to be formed. For lenses inabout the +2.0 to +4.0 diopter range, the front mold thickness ispreferably about 2.5-7.0 mm, more preferably about 3.0-5.0 mm, and morepreferably still about 3.5-4.0 mm, and the back mold thickness ispreferably about 2.0-5.0 mm, more preferably 2.0-4.0 mm, and morepreferably still about 2.5-3.0 mm. For lenses in about the zero("plano") to +2.0 diopter range, the front mold thickness is preferablyabout 2.5-8.0 mm, more preferably about 3.5-6.0 mm, and more preferablystill about 4.0-4.5 mm, and the back mold thickness is preferably about2.0-8.0 mm, more preferably 3.0-6.0 mm, and more preferably still about3.5-4.5 mm. For lenses in about the -2.0 to zero diopter range, thefront mold thickness is preferably about 2.0- 8.0 mm, more preferablyabout 3.0-6.0 mm, and more preferably still about 3.5-4.5 mm, and theback mold thickness is preferably about 2.5-8.0 mm, more preferably3.5-6.0 mm, and more preferably still about 4.0-4.5 mm. For lenses inabout the -4.0 to -2.0 diopter range, the front mold thickness ispreferably about 2.0-6.5 mm, more preferably about 2.6-5.0 mm, and morepreferably still about 3.2-4.0 mm, and the back mold thickness ispreferably about 2.0-8.0 mm, more preferably 3.0-6.0 mm, and morepreferably still about 4.0-4.5 mm. For lenses in about the -6.0 to -4.0diopter range, the front mold thickness is preferably about 2.0-5.0 mm,more preferably about 2.0-4.0 mm, and more preferably still about2.5-3.5 mm, and the back mold thickness is preferably about 2.0-8.0 mm,more preferably 3.0-6.0 mm, and more preferably still about 4.0-4.5 mm.

"Front" mold means the mold member with an inner surface that ultimatelyforms the surface of an eyeglass lens that is furthest from the eye ofan eyeglass lens wearer. "Back" mold means the mold member with an innersurface that ultimately forms the surface of an eyeglass lens that isclosest to the eye of a eyeglass lens wearer.

To minimize premature release and produce water-white ophthalmic lenses,preferably a lens is initially cured as described above. That is, a lensforming material is preferably initially cured at relatively lowtemperatures, relatively low ultraviolet light intensity, and relativelylow photoinitiator concentrations. "Initial" or "first" cure means thecure that transforms the liquid lens forming material into a solidmaterial. Lenses produced as such generally have a Shore D hardness ofabout 60-78 (for the preferred compositions) when cured for about 15minutes as described above. The hardness may be improved to about 80-81Shore D by postcure heating the lens in a conventional oven for about 10minutes, as described above. In the initial cure it is difficult toraise the hardness and surface cure of ultraviolet cured lenses abovethe levels described above. Achieving a higher degree of hardness andcure generally requires a faster, hotter reaction. The faster, hotterinitial cure reaction, however, tends to lead to poorer yields andlessened lens optical quality.

In a preferred embodiment of the invention, factors such as the level ofcure, rigidity, and hardness of ultraviolet light polymerized lenses maybe improved. A method of the invention to improve these factors involvesmaking a lens as described above, demolding the lens, and thensubjecting the lens to relatively high intensity ultraviolet lightpostcure conditions. This method may be carried out using a systempartially shown in FIG. 9 including: (i) an apparatus 300 for making aplastic lens which includes (1) a first mold member, (2) a second moldmember spaced apart from the first mold member, and the first and secondmold members defining a mold cavity, (3) a first ultraviolet lightgenerator for generating and directing ultraviolet light towards atleast one of the first and second mold members during use, (4) anultraviolet light filter disposed between the first ultraviolet lightgenerator and the first mold member, and between the first ultravioletlight generator and the second mold member, and (5) a distributor fordirecting cooling fluid towards the first and second mold members duringuse; (ii) a second ultraviolet light generator 304 for generating anddirecting ultraviolet light towards the lens during use; and (iii) afirst heater 306 to heat the lens during use. The system may alsoinclude a third ultraviolet light generator 308 for generating anddirecting ultraviolet light towards the lens during use after the lenshas been heated. The system may also include a second heater 310 forheating the lens during use after the third ultraviolet light generatorhas directed light towards the lens. The system may also include ademolder 302, which may simply include a small hammer and chisel.

In a preferred embodiment the second and third ultraviolet lightgenerators are the same generator. In a preferred embodiment the firstand second heaters are the same heater. In a preferred embodiment thefirst and second heater may be incorporated with the second and third UVlight generators. The system may also include additional heaters and orUV light generators.

Preferably the second and/or third ultraviolet light generators provideultraviolet light at an intensity of about 150-300 mW/cm², morepreferably about 175-250 mW/cm², at a wavelength range of about 360-370nm (preferably about 365 nm). Preferably the second and/or thirdultraviolet light generators provide ultraviolet light at an intensityof about 50-150 mW/cm², more preferably about 75-125 mW/cm², at awavelength range of about 250-260 nm (preferably about 254 nm). Thefirst or initial ultraviolet light generator preferably providesultraviolet light at a total intensity (from both sides) of less than 10mW/cm² (preferably about 0.3-2.0 mW/cm²). Thus preferably the second orthird ultraviolet light generators provide at least about 2, 5, 10, 20,40, 100, 500, 1000, and/or 1800 times the intensity of ultraviolet lightthan is provided by the first ultraviolet light generator. Preferablythese generators provide about 40-100, 100-500, 500-1800, 100-1800,and/or 40-1800 times the amount of light provided by the firstultraviolet light generator. Preferably the lens is exposed to theultraviolet light in the second, third and/or subsequent ultravioletlight generators for less than about 5 minutes, more preferably lessthan 1.0 minute, and more preferably still less than about 30 seconds.Preferably this exposure time is about 0.1-300 seconds, more preferablyabout 0.1-60 seconds, and more preferably still about 0.1-30 seconds. Inanother preferred embodiment the exposure time was less than 5 minutes.Generally as the intensity of the light is increased, the exposure timemay be decreased, and vice versa.

Preferably the lens is heated in the first or second heaters for lessthan about 180 minutes, more preferably less than 30 minutes, and morepreferably still less than about 10 minutes. Preferably the lens isheated in the second and/or third heaters at a temperature of about65°-180° C., more preferably about 85°-140° C., and more preferablystill about 100°-120° C. Generally as the temperature is decreased, theamount of heating time should be increased, and vice versa. In anotherpreferred embodiment the heating time was less than 5 seconds.

The lens is preferably cleaned (e.g., in a 50 volume % methanol/watersolution) prior to exposing the lens to the relatively high intensitylight. The relatively high intensity light may include relatively longand/or short wavelengths. The lens may then be heated. The lens may berepeatedly exposed to relatively high intensity ultraviolet light. Thelens may be repeatedly heated.

In a preferred embodiment, the high intensity light may be provided withmercury vapor lamps provided in a UVEXS, Inc. Model CCU curing chamber(Sunnyvale, Calif., U.S.A.).

It is believed that shorter wavelengths tend to improve the extent ofsurface cure and that longer wavelengths tend to increase the extent ofcure within the middle portions of the lens. Thus it is preferably touse both shorter and longer ultraviolet light wavelengths for the secondand third ultraviolet light generators. Exposure to the relatively highintensity UV wavelengths tends to yellow the lens, however subsequentlyheating the lens tends to reduce and/or eliminate this yellowing.Preferably the lens is heated to about 110°-120° C. Heating also allowsradicals to terminate and tends to increase the crosslinking of thecompounds within the lens. The polymerization strain also tends to bereduced during heating.

Lenses cured according to the above procedure exhibited a Shore Dhardness of above 83, with most lens about 83-85. These lenses also weremore rigid and tended to warp less when inserted into an eyeglass frameafter edging. There was negligible difference in the impact resistanceand scratch resistance of the lenses cured in this fashion, compared tolenses cured without exposure to the relatively high intensity UV light.It is anticipated that the postcure methods described above will tend toremedy lesser defects that may occur in the first cure using the firstUV light generator. For instance, the cure level for relatively low masslenses during the first cure may be less important since the postcurewill tend to ensure that the lenses are adequately cured. In like mannerdifferent lens compositions that do not cure to form ophthalmic qualitylenses in the first cure may be now usable since the postcure method mayincrease the quality of the cured lenses. For instance, the amount ofphotointiator and/or stabilizers in the initial composition may bevaried over a broader range and still achieve acceptable water-whitelenses.

In an alternate method for making a lens, the desired curvature (i.e.,power) of the lens may be varied using the same molds, but withdifferent light distributions. In this manner one mold may be used toprepare different lenses with different curvatures. The method includesthe steps of: (1) placing a polymerizable lens forming material in amold cavity defined in part between a first mold member and a secondmold member, and wherein the cavity defines a theoretical curvature thatis different from the desired curvature, (2) directing ultraviolet raystowards at least one of the first and second mold members, and whereinthe ultraviolet rays are directed towards the first or second moldmember such that the material cures to form a lens with the desiredcurvature, and (3) contacting fluid against the first or second moldmember to cool the first or second mold member. The resulting lenscurvature may vary depending on the way the ultraviolet light isdirected towards the first or second mold members. That is, by varyingthe relative intensity of the light across the lens material radii, itis possible to vary the curvature of the resulting lens.

Lens curvatures may also vary when the lenses are subjected to postcureheating. Thus the curvature of the lenses may be varied by exposing thelens material to UV light, and then demolding and heating the lens. Theheating may then result in the desired curvature, and this curvature maybe different from the theoretical curvature expected from the dimensionsof the mold cavity, as well as the curvature obtained after the lens hasbeen exposed to the initial UV light.

The present invention will now be described in more detail withreference to the following examples. These examples are merelyillustrative of the present invention and are not intended to belimiting.

EXAMPLE 1-LENS CURVATURE (POWER) VARIANCES

Lenses were produced under various conditions according to thecompositions, methods and apparatus of the present invention.

The formulation used to prepare the lenses according to this exampleincluded: 17.0% by weight of CR-73, 10.0% by weight of HDDMA, 21.0% byweight of TTEGDA, 32.0% by weight of TRPGDA, 20.0% by weight of TMPTA,0.0356% by weight of methyl benzoylformate, 0.0095% by weight ofIrgacure 184, and 0.16 ppm of Thermoplast Blue 684. The refractive indexof this formulation ranged from 1.468 to 1.478. The refractive index ofthe lenses produced according to this example ranged from 1.507 to1.511.

The method used to prepare the lenses according to this example wasthrough the mold irradiation with air-cooling.

The gaskets used to prepare the lenses according to this example were GESE6035 silicone rubber gaskets.

The molds used to prepare the lenses according to this example were madefrom Schott S-3 glass and had approximately parallel surfaces averaging4 mm in thickness.

The intensity of ultraviolet light from the top measured at the centerof the lens cell ranged from 0.35 mW/cm² to 0.37 mW/cm² for all lensesprepared according to this example. The ultraviolet lamps were kept at atemperature between 78 and 98 F.

For all lenses prepared according to this example, the upper lightfilter included 2 Pyrex glass sheets each frosted on one side with onesheet of tracing paper between them and the lower light filter alsoincluded 2 Pyrex glass sheets each frosted on one side with one sheet oftracing paper between them. In some cases the lower light filterincluded an opaque disc. The opaque disk tended to decrease the amountof light reaching the mold members, with the decrease maximized at thecenter of the mold members. The light tended to decrease in lesseramounts at points more distant from the center.

The following curing conditions were constant for all lenses preparedaccording to this example:

--ambient temperature--22° C.

--cooling air temperature--23.5° C.

--exit air flow rate at vent 33--20 ft³ /min.

--distance from disk to centerline of stage--38 mm.

The results are shown in Table 1 below. The results of this example forpositive lenses demonstrate that as the diameter of the opaque disk atthe lower light filter is increased: 1) the bottom light intensity isdecreased, 2) the flexing of both the front and back molds is increased,3) the power of the lenses before and after post-cure is reduced or lesspositive and, 4) the variance from the predicted power is reduced.

The results for negative lenses demonstrate that as the diameter of theopaque disk at the lower light filter is increased: 1) the bottom lightintensity is decreased, 2) the flexing of both the front and back moldswas essentially identical, 3) the power of the lenses before and afterpost-cure is increased or more negative, and, 4) the variance from thepredicted power is reduced.

                                      TABLE                                       __________________________________________________________________________         bottom light                 Variance                                         intensity                                                                            flexing                                                                             Power Power     from                                        disc in center                                                                            front                                                                            back                                                                             upon  upon Predicted                                                                          predicted                                   diameter                                                                           mW/cm.sup.2                                                                          mold                                                                             mold                                                                             demolding                                                                           postcure                                                                           Power                                                                              power                                       __________________________________________________________________________     0   .51    -.05                                                                             -.09                                                                             +1.82 +1.92                                                                              +1.80                                                                              +.12                                        21   .44    -.06                                                                             -.10                                                                             +1.76 +1.85                                                                              +1.80                                                                              +.05                                        39   .33    -.09                                                                             -.13                                                                             +1.66 +1.75                                                                              +1.80                                                                              -.05                                         0   .51    +.10                                                                             +.04                                                                             -1.80 -1.91                                                                              -1.98                                                                              +.07                                        21   .44    +.09                                                                             +.04                                                                             -1.86 -1.94                                                                              -1.99                                                                              +.05                                        39   .33    +.07                                                                             +.02                                                                             -1.90 -1.97                                                                              -1.99                                                                              +.02                                         0   .51    +.18                                                                             +.06                                                                             -3.72 -3.94                                                                              -4.02                                                                              +.08                                        21   .44    +.18                                                                             +.07                                                                             -3.74 -3.96                                                                              -4.02                                                                              +.06                                        39   .33    +.14                                                                             +.05                                                                             -3.83 -4.00                                                                              -4.02                                                                              +.02                                        __________________________________________________________________________

The results shown in Table 1 clearly demonstrate that the lensesproduced according to the present invention are in a stressed conditionafter ultraviolet light curing. The results also demonstrate that thestressed condition of the lenses may be reduced by an appropriatepost-curing heating step. The results also demonstrate that the power ofa finished lens produced according to the present invention may bealtered by manipulating the intensity of ultraviolet light incident on alens cell during the curing of a lens.

EXAMPLE 2-LIQUID COOLING

As noted above, according to one embodiment of the present invention,the lens cell 52 may be cooled by disposing it in a liquid cooling bath.According to this process a lens was cured under the followingconditions: The lens cell was made up of a 5.75 D front mold, a 7.50 Dback mold and a silicone rubber gasket. The lens forming composition was17% CR-73, 20% TMPTA, 21% TTEGDA, 32% TRPGDA, 10% HDDMA, 0.0336% MBZF,and 0.0084 Irgacure 184. The resultant center thickness was 2.4 mm. Thelens molding cavity 82 was filled with lens forming material and thelens cell was placed on a supporting stage in a bath of 85% H₂ O with15% propylene glycol at 0° C. A triangular array of ultraviolet lampswas utilized and the incident light intensity was 2.8 mW/cm² from thetop and 1.5 mW/cm² from the bottom. The lens cell was irradiated for 10minutes and the resultant lens had a measured focusing power of -1.80 D.The lens did not release and exhibited excellent stress patterns. TheShore D hardness was 67.

EXAMPLE 3-THROUGH THE GASKET CURING

As noted above, according to one embodiment of the present invention,the lens forming material can be polymerized by irradiating only throughthe gasket. The lens forming composition was 26% CR-73, 25% HDDMA, 16%TMPTA, 15% TTEGDA, 16% TRPGDA, 2% styrene, 0.03% Irgacure 184, and about0.3 ppm of Thermoplast Blue. According to this technique, a lens cellincluding a soft silicone rubber gasket configured for creating a -4.25D lens was suspended in the center of a cylindrical array of Sylvaniafluorescent F-15 8T/2052 lamps positioned at a distance from the lenscell to create an average light intensity of approximately 2 mW/cm² onthe gasket 80 of the lens cell 52. The sample was irradiated for 40minutes with 16 pounds of pressure being applied after 13 minutes ofirradiation. The pressure was later increased to a total of 21.5 pounds.The lens did not release, gave excellent stress patterns and goodoptics.

EXAMPLE 4-REDUCED TEMPERATURE CURING

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.012%   1 Hydroxycyclohexyl phenyl ketone                                    0.048    Methylbenzoylformate                                                <10 PPM   Hydroquinone & Methylethylhydro-                                              quinone                                                    ______________________________________                                    

Hydroquinone and Methylethylhydroquinone were stabilizers present insome of the diacrylate and/or triacrylate compounds obtained fromSartomer. Preferably the amount of stabilizers is minimized since thestabilizers affect the rate and amount of curing. If larger amounts ofstabilizers are added, then generally larger amounts of photoinitiatorsmust also be added.

Light Condition: mW/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.233   0.299                                                 Bottom:         0.217   0.248                                                 ______________________________________                                    

Air Flow: 9.6 standard cubic feet ("CFM") per manifold/19.2 CFM total onsample

Air Temperature: 4.4 degrees Centigrade

Molds: 80 mm diameter Corning #8092 glass

    ______________________________________                                                     Radius                                                                              Thickness                                                  ______________________________________                                        Concave:       170.59  2.7                                                    Convex:        62.17   5.4                                                    ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 2.2 mm.

Filling: The molds were cleaned and assembled into the gasket. Themold/gasket assembly was then temporarily positioned on a fixture whichheld the two molds pressed against the gasket lip with about 1 kg. ofpressure. The upper edge of the gasket was peeled back to allow about27.4 grams of the monomer blend to be charged into the cavity. The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device. It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop tends to cause the ultraviolet light to become locallyfocused and may cause an optical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber. The molds were separatedfrom the cured lens by applying a sharp impact to the junction of thelens and the convex mold. The sample was then postcured at 110° C. in aconventional gravity type thermal oven for an additional ten minutes,removed and allowed to cool to room temperature.

Results: The resulting lens measured 72 mm in diameter, with a centralthickness of 2.0 mm, and an edge thickness of 9.2 mm. The focusing powermeasured ˜5.05 diopter. The lens was water clear ("water-white"), showednegligible haze, exhibited total visible light transmission of about94%, and gave good overall optics. The Shore D hardness was about 80.The sample withstood the impact of a 1 inch steel ball dropped fromfifty inches in accordance with ANSI 280.1-1987, 4.6.4 test procedures.

EXAMPLE 5-REDUCED TEMPERATURE CURING

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.012%   1 Hydroxycyclohexyl phenyl ketone                                    0.048%   Methylbenzoylformate                                                <10 PPM   Hydroquinone & Methylethylhydro-                                              quinone                                                    ______________________________________                                    

Light Condition: mW/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.251   0.330                                                 Bottom:         0.236   0.265                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CM total on sample

Air temperature: 4.4 degrees Centigrade

Molds: 80 mm dia. Corning #8092 glass

    ______________________________________                                                     Radius                                                                              Thickness                                                  ______________________________________                                        Concave:       113.28  3.2                                                    Convex:        78.64   5.5                                                    ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providea initial cavity center thickness of 1.9 mm.

Filling: The molds were cleaned and assembled into the gasket, Themold/gasket assembly was them temporarily positioned on fixture whichheld the two molds pressed against the gasket lip with about 1 kg, ofpressure, The upper edge of the gasket was peeled back to allow about15.1 grams of the monomer blend to be charged into the cavity, The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device, It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop will cause the ultraviolet light to become locallyfocused too strongly on the monomer in the cavity and may cause anoptical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber. The molds were separatedfrom the cured lens by applying a sharp impact to the junction of thelens and the convex mold the sample was then postcured at 110 degrees C.in a conventional gravity type thermal oven for an additional tenminutes, removed and allowed to cool to room temperature.

Results: The resulting lens measured 73 mm in diameter, with a centralthickness of 1.7 mm, and an edge thickness of 4.3 mm. The focusing powermeasured ˜1.90 diopters. The lens was water clear, showed no haze,exhibited total visible light transmission of 94%, and gave good overalloptics. The Shore D hardness was 81. The sample withstood the impact ofa 7/8 inch steel ball dropped from fifty inches in accordance with ANSI280.1-1987, 4.6.4 test procedure.

EXAMPLE 6-REDUCED TEMPERATURE CURING

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.012%   1 Hydroxycyclohexyl phenyl ketone                                    0.048%   Methylbenzoylformate                                                <10 PPM   Hydroquinone & methylethylhydro-                                              quinone                                                    ______________________________________                                    

Light Condition: mW/cm² measured at plans of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.233   0.299                                                 Bottom:         0.217   0.248                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CFM total on sample

Air Temperature: 12.3 degrees Centigrade

Molds: 80 mm dia. Corning #8092 glass

    ______________________________________                                                    Radius  Thickness                                                 ______________________________________                                        Concave:      170.59 mm 2.7 mm                                                Convex:        62.17 mm 5.4 mm                                                ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 2.2 mm.

Filling: The molds were cleaned and assembled into the gasket. Themold/gasket assembly was then temporarily positioned on fixture whichheld the two molds pressed against the gasket lip with about 1 kg. ofpressure. The upper edge of the gasket was peeled back: to allow about27.4 grams of the monomer blend to be charged into the cavity. The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device. It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop will cause the ultraviolet light to become locallyfocused too strongly on the monomer in the cavity and may cause anoptical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber.

Results: The sample was found to have released from the front moldprematurely. The sample also showed signs of heat bubbling around theedges.

EXAMPLE 7-REDUCED TEMPERATURE CURING

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.012%   1 Hydroxycyclohexyl phenyl ketone                                    0.048%   Methylbenzoylformate                                                <10 PPM   Hydroquinone & Methylethylhydro-                                              quinone                                                    ______________________________________                                    

Light Condition: mW/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.251   0.330                                                 Bottom:         0.236   0.265                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CFM total on sample

Air Temperature: 12.3 degrees Centigrade

Molds: 80 mm dia. Corning #8092 glass

    ______________________________________                                                    Radius  Thickness                                                 ______________________________________                                        Concave:      123.28 mm 3.2 mm                                                Convex:        78.64 mm 5.5 mm                                                ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 1.9 mm.

Filling: The molds were cleaned and assembled into the gasket. Themold/gasket assembly was then temporarily positioned on fixture whichheld the two molds pressed against the gasket lip with about 1 kg. ofpressure. The upper edge of the gasket was peeled back to allow about15.1 grams of the monomer blend to be charged into the cavity. The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device. It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop will cause the ultraviolet light to become locallyfocused too strongly on the monomer in the cavity and may cause anoptical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber. The molds were separatedfrom the cured lens by applying a sharp impact to the junction of thelens and the convex mold. The sample was then postcured at 110 degreesC. in a conventional gravity type thermal oven for an additional tenminutes, removed and allowed to cool to room temperature.

Results: The resulting lens measured 73 mm in diameter, with a centralthickness of 1.7 mm, and an edge thickness of 4.3 mm. The focusing powermeasured ˜1.90 diopters. The lens was water clear, showed no haze,exhibited total visible light transmission of 94%, and gave good overalloptics. The Shore D hardness was 81. The sample withstood the impact ofa 7/8 inch steel ball dropped from fifty inches in accordance with ANSI280.1-1987, 4.6.4 test procedure.

EXAMPLE 8-REDUCED TEMPERATURE CURING

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.009%   1 Hydroxycyclohexyl phenyl ketone                                    0.036%   Methylbenzoylformate                                                <10 PPM   Hydroquinone & Methylethylhydro-                                              quinone                                                    ______________________________________                                    

Light Condition: mW/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.233   0.299                                                 Bottom:         0.217   0.248                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CFM total on sample

Air Temperature: 12.2 degrees Centigrade

Molds: 80 mm dia. Corning #8092 glass

    ______________________________________                                                    Radius  Thickness                                                 ______________________________________                                        Concave:      170.59 mm 2.7 mm                                                Convex:        62.17 mm 5.4 mm                                                ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 2.2 mm.

Filling: The molds were cleaned and assembled into the gasket. Themold/gasket assembly was then temporarily positioned on fixture whichheld the two molds pressed against the gasket lip with about 1 kg. ofpressure. The upper edge of the gasket was peeled back to allow about27.4 grams of the monomer blend to be charged into the cavity. The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device. It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop will cause the ultraviolet light to become locallyfocused too strongly on the monomer in the cavity and may cause anoptical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber. The molds were separatedfrom the cured lens by applying a sharp impact to the junction of thelens and the convex mold. The sample was then postcured at 110 degreesC. in a conventional gravity type thermal oven for an additional tenminutes, removed and allowed to cool to room temperature.

Results: The resulting lens measured 72 mm in diameter, with a centralthickness of 2.0 mm, and an edge thickness of 9.2 mm. The focusing powermeasured ˜5.05 diopters. The lens was water clear, showed no haze,exhibited total visible light transmission of 94%, and gave good overalloptics. The Shore D hardness was 80.5. The sample withstood the impactof a 1 inch steel ball dropped from fifty inches in accordance with ANSI280.1-1987, 4.6.4 test procedure.

EXAMPLE 9-REDUCED TEMPERATURE CURING

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.012%   1 Hydroxycyclohexyl phenyl ketone                                    0.048%   Methylbenzoylformate                                                <10 PPM   Hydroquinone & Methylethylhydro-                                              quinone                                                    ______________________________________                                    

Light Condition: mW/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.251   0.330                                                 Bottom:         0.236   0.265                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CFM total on sample

Air Temperature: 22.2 degrees Centigrade

Molds: 80 mm dia. Corning #8092 glass

    ______________________________________                                                    Radius  Thickness                                                 ______________________________________                                        Concave:      113.28 mm 3.2 mm                                                Convex:        78.64 mm 5.5 mm                                                ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 1.9 mm.

Filling: The molds were cleaned and assembled into the gasket. Themold/gasket assembly was then temporarily positioned on fixture whichheld the two molds pressed against the gasket lip with about 1 kg. ofpressure. The upper edge of the gasket was peeled back to allow about15.1 grams of the monomer blend to be charged into the cavity. The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device. It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop will cause the ultraviolet light to become locallyfocused too strongly on the monomer in the cavity and may cause anoptical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber. The molds were separatedfrom the cured lens by applying a sharp impact to the junction of thelens and the convex mold. The sample was then postcured at 110 degreesC. in a conventional gravity type thermal oven for an additional tenminutes., removed and allowed to cool to room temperature.

Results: The resulting lens measured 7.3 mm in diameter, with a centralthickness of 1.7 mm, and an edge thickness of 4.3 mm. The focusing powermeasured ˜1.87 diopters. The lens was water clear, showed no haze,exhibited total visible light transmission of 94%, and gave good overalloptics. The Shore D hardness was 83. The sample withstood the impact ofa 1 inch steel ball dropped from fifty inches in accordance with ANSI280.1-1987, 4.6.4 test procedure.

EXAMPLE 10-REDUCED TEMPERATURE CURING

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.009%   1 Hydroxycyclohexyl phenyl ketone                                    0.036%   Methylbenzoylformate                                                <10 PPM   Hydroquinone & Methylethylhydro-                                              quinone                                                    ______________________________________                                    

Light Condition: Mw/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.233   0.299                                                 Bottom:         0.217   0.248                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CFM total on sample

Air Temperature: 22.2 degrees Centigrade

Molds: 80 mm dia. Corning #8092 glass

    ______________________________________                                                    Radius  Thickness                                                 ______________________________________                                        Concave:      170.59 mm 2.7 mm                                                Convex:        62.17 mm 5.4 mm                                                ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 2.2 mm.

Filling: The molds were cleaned and assembled into the gasket. Themold/gasket assembly was then temporarily positioned on fixture whichheld the two molds pressed against the gasket lip with about 1 kg. ofpressure. The upper edge of the gasket was peeled back to allow about27.4 grams of the monomer blend to be charged into the cavity. The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device. It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop will cause the ultraviolet light to become locallyfocused too strongly on the monomer in the cavity and may cause anoptical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber.

Results: The sample was found to have released from the moldsprematurely. It also showed heat bubbles at the edge.

EXAMPLE 11-HIGH INTENSITY UV POSTCURE-1 COMPOSITION

A number of lenses were prepared with the same physical molds andgasket, with the same lens forming composition, and under identicalinitial UV light curing conditions. These lenses were then subjected tovarious combinations of second and/or third UV intensity/time andtemperature/time conditions. The results for Shore D hardness and impactresistance of each lens are shown in Table 2. The second or third UVsource was a UVEXS CCU curing chamber configured with a medium pressurevapor lamp, a collimated dichroic reflector which reduced the IRradiation of the lamp by 50%, and two selectable output levels. The lowsetting provides approximately 175 mW/cm² at about 365 nm and 70 mW/cm²at about 254 nm. The high setting produces about 250 mW/cm² at about 365nm and 100 mW/cm² at about 254 nm. The initial curing conditions areidentified below.

    ______________________________________                                        Formulation:                                                                           17%       Bisphenol A BisAllyl Carbonate                                      10%       1,6 Hexanediol dimethacrylate                                       20%       Trimethylolpropane triacrylate                                      21%       Tetraethyleneglycol diacrlate                                       32%       Tripropyleneglycol diacrlyate                                        0.012%   1 Hydroxycyclohexyl phenyl ketone                                    0.048%   Methylbenzoylformate                                                <10 PPM   Hydroquinone & Methylethylhydro-                                              quinone                                                    ______________________________________                                    

Initial Cure

Light Condition: Mw/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.251   0.330                                                 Bottom:         0.236   0.265                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CFM total on sample

Air Temperature: 4.8 degrees Centigrade

Molds: 80 mm dia. Corning #8092 glass

    ______________________________________                                                     Radius                                                                              Thickness                                                  ______________________________________                                        Concave:       113.28  3.2                                                    Convex:        78.52   5.2                                                    Lens Power:          -1.90   D                                                Lens Thickness:      2.2     mm                                               Lens Diameter:       73      mm                                               ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 2.4 mm.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber. The molds were separatedfrom the cured lens by applying a sharp impact to the junction of thelens and the convex mold. The sample was then postcured as described.Unless otherwise indicated, the stated "hard" or high intensity UVpostcure time/intensity doses were applied twice--i.e., first to theconvex surface and then to the concave surface for each exposure. Forexample, if the dose is described as "14 sec/low", it means that thefront surface of the lens was exposed for 1.4 seconds to the lowintensity rays and then the lens was turned over and the back wasexposed for the same length of time to the same intensity level oflight. The term "CX" means convex, the term "CC" means concave, the term"HD" means Shore D hardness, "pass" means the lens passed the 1" steelball impact resistance test described in the previous examples (seee.g., example 9), "2nd UV" means the first UV postcure light (theinitial cure was the "1st UV"), and "3rd UV" means the second UVpostcure light. Time units are in minutes, unless "sec" for seconds isspecified. Temperature is defined in degrees Centigrade.

                                      TABLE 2                                     __________________________________________________________________________    HIGH INTENSITY UV/THERMAL POSTCURE EXAMPLES                                      2nd UV 1st Thermal                                                                          3rd UV Lamp                                                                           2nd Thermal Impact                                      Lamp Time/                                                                           Postcure                                                                             Time/   Postcure                                                                             Shore D                                                                            1"                                       #  Intensity                                                                            Time/Temp                                                                            Intensity                                                                             Time/Temp                                                                            Hardness                                                                           Ball                                     __________________________________________________________________________    1  0      0      0       0      65   --                                       2  0      10:00/115° C.                                                                 0       0      80   Pass                                     3  1.4 sec/                                                                             10:00/115° C.                                                                 0       0      82   7/8"                                        low                                                                        4  0      5:00/115° C.                                                                  1.4 sec/low                                                                           5:00/115 C.                                                                          83   Pass                                     5  1.4 sec/                                                                             5:00/115° C.                                                                  1.4 sec/low                                                                           5:00/115 C.                                                                          85   Pass                                        low                                                                        6  1.4 sec/                                                                             5:00/65° C.                                                                   1.4 sec/low                                                                           5:00/65 C.                                                                           80   Pass                                        low                                                                        7  1.4 sec/                                                                             5:00/65° C.                                                                   1.4 sec/low                                                                           15:00/65 C.                                                                          81   Pass                                        low                                                                        8  1.4 sec/                                                                             5:00/65° C.                                                                   1.4 sec/low                                                                           25:00/65 C.                                                                          81   Pass                                        low                                                                        9  1.4 sec/                                                                             5:00/80° C.                                                                   1.4 sec/low                                                                           5:00/80 C.                                                                           82   Pass                                        low                                                                        10 1.4 sec/                                                                             5:00/140° C.                                                                  1.4 sec/low                                                                           5:00/140 C.                                                                          85   Pass                                        low                                                                        11 1.4 sec/                                                                             5:00/180° C.                                                                  1.4 sec/low                                                                           5:00/180 C.                                                                          85   Pass                                        low                                                                        12 12.0 sec/                                                                            0      0       0      80   Pass                                        high                                                                       13 12.0 sec/                                                                            1:00/180° C.                                                                  0       0      83   Pass                                        high                                                                       14 12.0 sec/                                                                            10:00/115° C.                                                                 0       0      85   Pass                                        high                                                                       15 12.0 sec/                                                                            30:00/65° C.                                                                  0       0      83   Pass                                        high                                                                       16 12.0 sec/                                                                            10:00/115° C.                                                                 1.0 sec/low                                                                           0      85   Pass                                        high                                                                       17 1.0 sec/                                                                             5:00/115° C.                                                                  1.0 sec/low                                                                           5:00/115 C.                                                                          83   Pass                                        low           (Exposed CX                                                     (Exposed      side 1×                                                   CX side 1×                                                                            only, CC                                                        only, CC      side 0                                                          side 0        times)                                                          times)                                                                     __________________________________________________________________________

EXAMPLE 12-HIGH INTENSITY UV POSTCURE-VARIOUS COMPOSITIONS

A number of lenses made from different compositions were prepared withthe same physical molds and gasket, and under identical initial curingconditions. The lenses were then subjected to fixed postcure procedures;with fixed UV intensity/time and temperature/time conditions. It shouldbe noted that each of the acrylic components were passed through analumina column to remove impurities and inhibitors before use. Theresults for Shore D hardness after the postcure, and the impactresistance of each product are shown in Table 3. The postcure UV sourceused was a UVEXS CCU curing chamber configured with a medium pressurevapor lamp, a collimated dichroic reflector which reduced the IRradiation of the lamp by 50%, and two selectable output levels. The lowsetting provides approximately 175 mW/cm² at about 365 nm and 70 mW/cm²at about 254 nm. The high setting produces about 250 mW/cm² at about 365mn and 100 mW/cm² at about 254 nm. The initial curing conditions areidentified below.

Initial Cure

Light Condition: Mw/cm² measured at plane of sample

    ______________________________________                                                      Center                                                                              Edge                                                      ______________________________________                                        Top:            0.233   0.299                                                 Bottom:         0.217   0.248                                                 ______________________________________                                    

Air Flow: 9.6 CFM per manifold/19.2 CFM total on sample

Air Temperature: 4.8 degrees Centigrade

Molds 80 mm dia. Corning #8092 glass

    ______________________________________                                                     Radius                                                                              Thickness                                                  ______________________________________                                        Concave:       113.22  3.2                                                    Convex:        78.52   5.2                                                    Lens Power:          -1.90   D                                                Lens Thickness:      2.2     mm                                               Lens Diameter:       73      mm                                               ______________________________________                                    

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 2.4 mm.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the curing chamber. The molds were separatedfrom the cured lens by applying a sharp impact to the junction of thelens and the convex mold. The lens was then postcured by first exposingit to the low power setting in the UVEXS curing chamber (1.4 secondseach side after demolding). The sample was then placed in the thermaloven for five minutes at 115 degrees Centigrade, removed from the oven,and once again exposed for 1.4 seconds to the postcure UV at the lowpower setting. It was then returned to the thermal oven for another fiveminutes at 115 degrees Centigrade. The postcure UV doses were appliedfirst to the convex surface and then to the concave surface for eachexposure. For example, if the dose is described as "1.4 sec/low", itmeans that the front surface of the lens was exposed for 1.4 seconds tothe low intensity and then the lens was turned over and the back wasexposed for the same length of time at the same intensity level. Theimpact resistance ("I/R") of each lens was pursuant to ANSI standards,as described for the other examples. The lenses were first tested with a5/8" diameter steel ball bearing, a 7/8" steel ball bearing, and then a1" steel ball bearing. The maximum diameter of ball bearing that thesample survived the impact of is described below. "CR-73" meansbispherol A bis(allyl carbonate), "MBZF" means methyl benzoylformate,"Irg. 184" means Irgacure 184.

                                      TABLE 3                                     __________________________________________________________________________                              Shore D                                                                       hardness                                                                           Final                                                          % Irg.                                                                             Total                                                                              after 1st                                                                          Shore D                                        Composition                                                                             % MBZF                                                                              184  Pi % UV   Hardness                                                                           I/R                                       __________________________________________________________________________    CR-73 20% 0.086 0.265                                                                              0.351                                                                              57   85-86                                                                              1"                                        HDDMA 80%                                                                     CR-73 20% 0.0257                                                                              0.0064                                                                             0.0321                                                                             55   70   1"                                        TTEGDA                                                                              80%                                                                     CR-73 20% 0.025 0.0062                                                                             0.031                                                                              48   75   1"                                        TRPGDA                                                                              80%                                                                     CR-73 20% 0.0461                                                                              0.0115                                                                             0.0576                                                                             50   87   5/8"                                      TMPTA 80%                                                                     TMPTA 90% 0.054 0.014                                                                              0.068                                                                              72   88   7/8"                                      TRPGDA                                                                              10%                                                                     TRPGDA                                                                              90% 0.0274                                                                              0.0068                                                                             0.0342                                                                             68-70                                                                              82   1"                                        TMPTA 10%                                                                     TMPTA 36.5%                                                                             0.096 0.048                                                                              0.144                                                                              68   87   1"                                        HDDMA 24.4%                                                                   TRPGDA                                                                              39.1%                                                                   TMPTA 30% 0.062 0.021                                                                              0.083                                                                              67   87   1"                                        HDDMA 10%                                                                     TRPGDA                                                                              60%                                                                     TMPTA 30% 0.0295                                                                              0.0074                                                                             0.0369                                                                             65   85   1"                                        CR-73 15%                                                                     TTEGDA                                                                              22%                                                                     TRPGDA                                                                              33%                                                                     HDDMA 100%                                                                              0.108 0.331                                                                              0.439                                                                              64-66                                                                              86-87                                                                              1"                                        HDDMA 94% 0.12  0.16 0.28 50   86   1"                                        CR-73 1.14%                                                                   TMPTA 1.34%                                                                   TTEGDA                                                                              1.41%                                                                   TRPGDA                                                                              2.14%                                                                   TTEGDA                                                                              100%                                                                              0.01  0.0025                                                                             0.0125                                                                             58-60                                                                              77   1"                                        TTEGDA                                                                              98.4%                                                                             0.059 0.015                                                                              0.074                                                                              70   78   1"                                        CR-73 0.3%                                                                    HDDMA 0.2%                                                                    TMPTA 0.4%                                                                    TRPGDA                                                                              0.6%                                                                    TRPGDA                                                                              100%                                                                              0.024 0.006                                                                              0.030                                                                              66   81-82                                                                              1"                                        CR-73 0.13%                                                                             0.0238                                                                              0.006                                                                              0.0244                                                                             67   82   1"                                        HDDMA 0.10%                                                                   TMPTA 0.15%                                                                   TTEGDA                                                                              0.16%                                                                   TRPGDA                                                                              99.5%                                                                   TMPTA 100%                                                                              0.058 0.014                                                                              0.072                                                                              56   89-91                                                                              1"                                        TTEGDA                                                                              0.38%                                                                             0.056 0.014                                                                              0.070                                                                              46   87   7/8"                                      CR-73 0.31%                                                                   HDDMA 0.20%                                                                   TMPTA 98.6%                                                                   TRPGDA                                                                              0.58%                                                                   HDDMA 100%                                                                              0.668 --   0.668                                                                              45   87   5/8"                                      HDDMA 100%                                                                              1.215 --   1.215                                                                              40   85   5/8"                                      TTEGDA                                                                              100%                                                                              0.018 --   .018 65   77   1"                                        TRPGDA                                                                              100%                                                                              0.0441                                                                              --   .0441                                                                              67   80   1"                                        TMPTA 100%                                                                              0.064 --   0.064                                                                              60   87   1"                                        TMPTA 100%                                                                              0.093 --   0.093                                                                              70   91   7/8"                                      CR-73  14.5%                                                                            0.0377                                                                              --   0.0377                                                                             60   80   1"                                        TRPGDA                                                                              85.5%                                                                   CR-73 13.6%                                                                             0.074 --   0.074                                                                              52   85   1"                                        TMPTA 86.4%                                                                   TMPTA 31.6%                                                                             0.0205                                                                              --   0.0205                                                                             70   84   1"                                        TTEGDA                                                                              37.2%                                                                   TRPGDA                                                                              16.7%                                                                   CR-73 14.5%                                                                   __________________________________________________________________________

The initial UV curing time for each lens was 15 minutes, with theexception of the compositions with only TTEGDA with MBZF and Irgacure184 (which had an initial curing time of 20 minutes), the compositionswith only HDDMA and MBZF (which had an initial curing time of 45minutes), the composition with only CR-73, TMPTA, and MBZF (which had aninitial curing time of 20 minutes). The lenses that resulted weregenerally all water-white optically clear lenses with negligibleyellowing and negligible haziness. The 100% TMPTA and 98.6% TMPTA lenseswere slightly yellow but otherwise they were the same as the otherlenses. These slightly yellow lens formulations may have the yellownessreduced with the addition of an effective amount of Thermoplast Blueadded to the formulation.

Generally speaking, the single component (or primarily single component)lenses had generally less preferred optical qualities. Some of theselenses had slight wave patterns in some portions of the lenses.

It is thus seen that the methods, apparatus and compositions of thepresent invention provide several advantages. For example, according tocertain embodiments of the present invention a plastic optical lens canbe cured in 30 minutes or less. Furthermore, in certain embodiments ofthe present invention, the lens composition includes monomers having ahigher refractive index than conventional monomer materials allowing theproduction of thinner lenses.

Although not specifically illustrated in the drawings, it is understoodthat other additional and necessary equipment and structural componentswill be provided, and that these and all of the components describedabove are arranged and supported in an appropriate fashion to form acomplete and operative system.

It is also understood that variations may be made in the presentinvention without departing from the spirit and scope of the invention.Of course, other variations can be made by those skilled in the artwithout departing from the invention as defined by the appended claims.

What is claimed is:
 1. A method for making a plastic lens, comprising:a) placing a polymerizable lens forming material in a mold cavitydefined in part between a first mold member with a thickness of about1.0-5.0 mm and a second mold member with a thickness of about 1.0-5.0mm; and b) directing ultraviolet rays towards at least one of the firstor second mold members while substantially simultaneously cooling thefirst mold member and the second mold member with air at a temperatureof between 0° C. and less than 20° C. which is directed at a rate ofabout 1-30 standard cubic feet (about 0.028-0.850 standard cubic meters)per minute toward the first mold member to cool the first mold member,and which is directed at a rate of about 1-30 standard cubic feet (about0.028-0.850 standard cubic meters) per minute toward the second moldmember to cool the second mold member.
 2. The method of claim 1 whereinthe air temperature is about 0°-15° C.
 3. The method of claim 1 whereinthe air temperature is about 0°-10° C.
 4. The method of claim 1 whereinthe air temperature is about 3°-8° C.
 5. The method of claim 1 whereinthe mold cavity is substantially cylindrical and the height of thecavity varies across the diameter of the cavity; and wherein theintensity of the ultraviolet rays is varied approximately in proportionto the height of the cavity.
 6. The method of claim 1 wherein the firstand second mold members each have a face, and the air is directed towardthe face of the first mold member, and toward the face of the secondmold member.
 7. The method of claim 1 wherein the first and second moldmembers each have a center and edges, and the air is directed from theedges of the first mold member to the center of the first mold member,and from the edges of the second mold member to the center of the secondmold member.
 8. The method of claim 1 wherein the rate of air contactingthe first mold member is about 4-20 standard cubic feet (about0.113-0.566 standard cubic meters) per minute, and the rate of aircontacting the second mold member is about 4-20 standard cubic feet(about 0.113-0.566 standard cubic meters) per minute.
 9. The method ofclaim 1 wherein the rate of air contacting the first mold member isabout 9-15 standard cubic feet (about 0.255-0.423 standard cubic meters)per minute, and the rate of air contacting the second mold member isabout 9-15 standard cubic feet (about 0.255-0.423 standard cubic meters)per minute.
 10. The method of claim 1 wherein the first or second moldmember has a thickness of about 2.0-4.0 mm.
 11. The method of claim 1wherein the first or second mold member has a thickness of about 2.5-3.5mm.
 12. A method for making a plastic lens with a desired curvature,comprising:placing a polymerizable lens forming material in a moldcavity defined at least in part between a first mold member and a secondmold member, and wherein the cavity defines a theoretical lens curvaturethat is different from the desired curvature; and directing ultravioletrays towards at least one of the first and second mold members such thatportions of the material in the cavity receive different intensities ofultraviolet light from other portions of the material in the cavity,thereby allowing the material to cure to form a lens with the desiredcurvature.
 13. The method of claim 12, further comprising demolding thelens and heating the lens.
 14. The method of claim 13 wherein theheating forms the lens with a second desired curvature.
 15. The methodof claim 12 wherein the intensity of the ultraviolet rays is variedacross the first or second mold members such that the material cures toform the lens with the desired curvature.
 16. A method for making aplastic lens, comprising:a) placing a polymerizable lens formingmaterial in a mold cavity defined in part between a first mold memberand a second mold member; and b) directing ultraviolet rays towards atleast one of the first or second mold members while substantiallysimultaneously c) cooling the first mold member and the second moldmember with air at a temperature of less than 20° C. which is directedat a rate of about 1-30 standard cubic feet (about 0.028-0.850 standardcubic meters) per minute toward the first mold member to cool the firstmold member, and which is directed at a rate of about 1-30 standardcubic feet (about 0.028-0.850 standard cubic meters) per minute towardthe second mold member to cool the second mold member.
 17. The method ofclaim 16, further comprising directing first ultraviolet rays at a totalintensity of less than about 10 mW/cm² toward at least one of the moldmembers to cure the material to a lens while substantiallysimultaneously contacting fluid against the first or second mold memberto cool the first or second mold member; anddirecting second ultravioletrays towards the lens at an intensity of about 150-300 mW/cm² at awavelength range of about 360-370 nm, and about 50-150 mW/cm² at awavelength range of about 250-260 nm.
 18. The method of claim 17,further comprising directing third ultraviolet rays towards the lens.19. The method of claim 18, further comprising heating the lens afterthe third ultraviolet rays are directed towards the lens.
 20. The methodof claim 19 wherein the lens is heated to a temperature of about65°-180° C.
 21. The method of claim 19 wherein the lens is heated forless than about 30 minutes.
 22. The method of claim 17 wherein thesecond ultraviolet rays are directed at the lens for less than about 1minute.
 23. The method of claim 18 wherein the intensity of the thirdultraviolet rays is about 150-300 mW/cm² at a wavelength range of about360-370 nm, and about 50-150 mW/cm² at a wavelength range of about250-260 nm.
 24. The method of claim 18 wherein the third ultravioletrays are directed at the lens for less than about 1 minute.
 25. Themethod of claim 19 wherein the lens is heated to a temperature of about65°-180° C. after the third ultraviolet rays are directed towards thelens.
 26. The method of claim 19 wherein the lens is heated for lessthan about 30 minutes after the third ultraviolet rays are directedtowards the lens.
 27. The method of claim 16, further comprisingdirecting rays of ultraviolet light through an annular gasket to curethe lens forming material.
 28. The method of claim 27, furthercomprising preventing rays of ultraviolet light from impinging againstthe first or second mold members.
 29. The method of claim 12, furthercomprising cooling the material in the lens cavity.
 30. The method ofclaim 12, further comprising cooling the material in the lens cavitywhile substantially simultaneously directing ultraviolet rays towards atleast one of the first and second mold members.
 31. The method of claim12, further comprising cooling the material in the lens cavity bydirecting air towards at least one of the first and second mold memberswhile substantially simultaneously directing ultraviolet rays towards atleast one of the first and second mold members.
 32. The method of claim12, further comprising cooling the material in the lens cavity bydirecting air at a temperature of less than 20° C. towards at least oneof the first and second mold members while substantially simultaneouslydirecting ultraviolet rays towards at least one of the first and secondmold members.
 33. The method of claim 12, further comprising cooling thematerial in the lens cavity by directing air at a temperature of between0°-15° C. towards at least one of the first and second mold memberswhile substantially simultaneously directing ultraviolet rays towards atleast one of the first and second mold members.
 34. The method of claim12 wherein the mold cavity is substantially cylindrical and the heightof the cavity varies across the diameter of the cavity, and wherein theintensity of the ultraviolet rays is varied approximately in proportionto the height of the cavity.
 35. The method of claim 31 wherein the moldcavity is substantially cylindrical and the height of the cavity variesacross the diameter of the cavity, and wherein the intensity of theultraviolet rays is varied approximately in proportion to the height ofthe cavity.
 36. The method of claim 12 wherein the first and second moldmembers each have a face, and air is directed toward the face of thefirst mold member, and toward the face of the second mold member. 37.The method of claim 31 wherein the first and second mold members eachhave a face, and air is directed toward the face of the first moldmember, and toward the face of the second mold member.
 38. The method ofclaim 12 wherein the first and second mold members each have a centerand edges, and air is directed from the edges of the first mold memberto the center of the first mold member.
 39. The method of claim 31wherein the first and second mold members each have a center and edges,and air is directed from the edges of the first mold member to thecenter of the first mold member.
 40. The method of claim 12 wherein thefirst and second mold members each have a center and edges, and air isdirected from the edges of the first mold member to the center of thefirst mold member, and from the edges of the second mold member to thecenter of the second mold member.
 41. The method of claim 31 wherein thefirst and second mold members each have a center and edges, and air isdirected from the edges of the first mold member to the center of thefirst mold member, and from the edges of the second mold member to thecenter of the second mold member.
 42. The method of claim 12 wherein thefirst and second mold members each have a center and edges, and air isdirected from the center of the first mold member to the edges of thefirst mold member.
 43. The method of claim 31 wherein the first andsecond mold members each have a center and edges, and air is directedfrom the center of the first mold member to the edges of the first moldmember.
 44. The method of claim 12 wherein the first and second moldmembers each have a center and edges, and air is directed from thecenter of the first mold member to the edges of the first mold member,and from the center of the second mold member to the edges of the secondmold member.
 45. The method of claim 31 wherein the first and secondmold members each have a center and edges, and air is directed from thecenter of the first mold member to the edges of the first mold member,and from the center of the second mold member to the edges of the secondmold member.
 46. The method of claim 12 wherein the ultraviolet light isfiltered such that different intensities of it are applied to differentportions of the material in the cavity.
 47. The method of claim 46wherein the ultraviolet light is filtered with a filter which comprisesa disk of opaque material for reducing the intensity of ultravioletlight reaching the center of the mold members relative to the intensityof ultraviolet light reaching the edge of the mold members during use.48. The method of claim 46 wherein the ultraviolet light is filteredwith a filter which comprises a-ring of opaque material for reducing theintensity of ultraviolet light reaching the edge of the mold membersrelative to the intensity of ultraviolet light reaching the center ofthe mold members during use.
 49. The method of claim 46 wherein theultraviolet light is filtered with a filter which comprises atransparent sheet material having a plurality of ultraviolet lightabsorbing shapes printed thereon.
 50. The method of claim 49 wherein thedensity per unit area of the shapes is at a minimum at a pointcorresponding to the greatest distance between the first mold member andthe second mold member and wherein the density per unit area of theshapes is at a maximum at a point corresponding to the smallest distancebetween the first mold member and the second mold member.
 51. The methodof claim 31 wherein the air is directed through a distributor whichcomprises an air jet having a substantially cylindrical bore, and thebore has a plurality of openings disposed about the circumferencethereof.
 52. The method of claim 51 wherein the average diameter of theopenings in the air jet varies about the circumference of the bore. 53.The method of claim 51 wherein the air jet comprises an air inlet andthe diameter of the openings is at a minimum adjacent the air inlet, andthe diameter of the openings is at a maximum at a point along thecircumference of the bore that is opposite the bores having a minimumdiameter.
 54. The method of claim 12, further comprising directingsecond ultraviolet rays towards the lens, thereby forming a lens with asecond desired curvature.
 55. The method of claim 13, further comprisingdirecting second ultraviolet rays towards the lens, thereby forming alens with a second desired curvature.
 56. The method of claim 12 whereinthe ultraviolet rays are at a total intensity of less than about 10mW/cm², and further comprising the step of directing second ultravioletrays towards the lens at an intensity of about 150-300 mW/cm² at a peakwavelength between 360-370 nm, and about 50-150 mW/cm² at a peakwavelength between 250-260 nm, thereby forming a lens with a seconddesired curvature.
 57. The method of claim 13 wherein the ultravioletrays are at a total intensity of less than about 10 mW/cm², and furthercomprising the step of directing second ultraviolet rays towards thelens at an intensity of about 150-300 mW/cm² at a peak wavelengthbetween 360-370 nm, and about 50-150 mW/cm² at a peak wavelength between250-260 nm, thereby forming a lens with a second desired curvature. 58.The method of claim 55 wherein the second ultraviolet rays are directedtowards the lens for a time period of less than about one minute. 59.The method of claim 13 wherein the lens is heated to a temperature ofabout 65°-180° C. for less than about 30 minutes.
 60. The method ofclaim 12, wherein the material comprises at least onepolyethylenic-functional monomer containing two ethylenicallyunsaturated groups selected from acrylyl and methacrylyl.
 61. The methodof claim 60 wherein the material further comprises an aromaticcontaining bis(allyl carbonate)-functional monomer.
 62. The method ofclaim 12 wherein the material comprises at least onepolyethylenic-functional monomer containing three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl.
 63. The methodof claim 62 wherein the material further comprises an aromaticcontaining bis(allyl carbonate)-functional monomer.
 64. The method ofclaim 12, further comprising selecting the first mold and the secondmold such that the cavity defines a theoretical curvature which, whenthe ultraviolet light is directed at the material, will cause thematerial to form a lens with the desired curvature.
 65. The method ofclaim 12 wherein portions of the material in the cavity receivedifferent intensities of ultraviolet light from other portions of thematerial in the cavity, thereby causing the material to cure to form alens with the desired curvature.
 66. The method of claim 12 wherein atleast one mold member has a center and edges, and wherein the intensityof the light received by portions of the material proximate the moldcenter is less than the intensity of light received by portions of thematerial proximate a mold edge, thereby causing the material to form alens with more negative power than the power of the lens with thetheoretical curvature.
 67. The method of claim 12 wherein at least onemold member has a center and edges, and wherein the intensity of thelight received by portions of the material proximate the mold center ismore than the intensity of light received by portions of the materialproximate a mold edge, thereby causing the material to form a lens withless negative power than the power of the lens with the theoreticalcurvature.
 68. The method of claim 12 wherein at least one mold memberhas a center and edges, and wherein the intensity of the light receivedby portions of the material proximate the mold center is less than theintensity of light received by portions of the material proximate a moldedge, thereby causing the material to form a lens with less positivepower than the power of the lens with the theoretical curvature.
 69. Themethod of claim 12 wherein at least one mold member has a center andedges, and wherein the intensity of the light received by portions ofthe material proximate the mold center is more than the intensity oflight received by portions of the material proximate a mold edge,thereby causing the material to form a lens with more positive powerthan the power of the lens with the theoretical curvature.
 70. Themethod of claim 1 wherein the first and second mold members each have acenter and edges, and air is directed from the edges of the first moldmember to the center of the first mold member.
 71. The method of claim 1wherein the first and second mold members each have a center and edges,and air is directed from the center of the first mold member to theedges of the first mold member.
 72. The method of claim 1 wherein theultraviolet light is filtered such that different intensities of it areapplied to different portions of the material in the cavity.
 73. Themethod of claim 72 wherein the ultraviolet light is filtered with afilter which comprises a disk of opaque material for reducing theintensity of ultraviolet light reaching the center of the mold membersrelative to the intensity of ultraviolet light reaching the edge of themold members during use.
 74. The method of claim 72 wherein theultraviolet light is filtered with a filter which comprises a ring ofopaque material for reducing the intensity of ultraviolet light reachingthe edge of the mold members relative to the intensity of ultravioletlight reaching the center of the mold members during use.
 75. The methodof claim 72 wherein the ultraviolet light is filtered with a filterwhich comprises a transparent sheet material having a plurality ofultraviolet light absorbing shapes printed thereon.
 76. The method ofclaim 75 wherein the density per unit area of the shapes is at a minimumat a point corresponding to the greatest distance between the first moldmember and the second mold member and wherein the density per unit areaof the shapes is at a maximum at a point corresponding to the smallestdistance between the first mold member and the second mold member. 77.The method of claim 1 wherein the air is directed through a distributorwhich comprises an air jet having a substantially cylindrical bore, andthe bore has a plurality of openings disposed about the circumferencethereof.
 78. The method of claim 77 wherein the average diameter of theopenings in the air jet varies about the circumference of the bore. 79.The method of claim 77 wherein the air jet comprises an air inlet andthe diameter of the openings is at a minimum adjacent the air inlet, andthe diameter of the openings is at a maximum at a point along thecircumference of the bore that is opposite the bores having a minimumdiameter.
 80. The method of claim 1 wherein the ultraviolet rays are ata total intensity of less than about 10 mW/cm², and further comprisingthe step of directing second ultraviolet rays towards the lens at anintensity of about 150-300 mW/cm² at a peak wavelength between 360-370nm, and about 50-150 mW/cm² at a peak wavelength between 250-260 nm. 81.The method of claim 80 wherein the second ultraviolet rays are directedtowards the lens for a time period of less than about one minute. 82.The method of claim 1, further comprising heating the lens to atemperature of about 65°-180° C. for less than about 30 minutes.
 83. Themethod of claim 1, wherein the; material comprises at least onepolyethylenic-functional monomer containing two ethylenicallyunsaturated groups selected from acrylyl and methacrylyl.
 84. The methodof claim 83 wherein the material further comprises an aromaticcontaining bis(allyl carbonate)-functional monomer.
 85. The method ofclaim 1 wherein the material comprises at least onepolyethylenic-functional monomer containing three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl.
 86. The methodof claim 85 wherein the material further comprises an aromaticcontaining bis(allyl carbonate)-functional monomer.
 87. The method ofclaim 12, further comprising directing different intensities ofultraviolet light towards different portions of at least one of thefirst and second mold members.
 88. The method of claim 87 wherein theintensity of ultraviolet light directed towards a center of at least oneof the first and second mold members is greater than the intensity ofultraviolet light directed towards an edge of at least one of the firstand second mold members.
 89. The method of claim 87 wherein theintensity of ultraviolet light directed towards a center of at least oneof the first and second mold members is less than the intensity ofultraviolet light directed towards an edge of at least one of the firstand second mold members.
 90. The method of claim 87, further comprisingdetermining a desired curvature of the lens, and, based on thisdetermination, selecting different intensities of light to directtowards different portions of at least one of the first and second moldmembers.
 91. The method of claim 31, further comprising determining thedesired curvature of the lens, and, based on this determination,selecting different intensities of light to direct towards at least oneof the first and second mold members, and then directing the differentintensities of ultraviolet light towards different portions of at leastone of the first and second mold members.
 92. The method of claim 12,further comprising directing a first set of ultraviolet light towards alens forming composition in the cavity to form a first lens with a firstdesired lens curvature, and directing a second set of ultraviolet lighttowards a lens forming composition in the same cavity to form a secondlens with a second desired lens curvature, the first set of ultravioletlight being different from the second set of ultraviolet light, and thefirst desired lens curvature being different from the second desiredlens curvature.
 93. The method of claim 92, further comprisingdetermining a desired curvature, and, based on this determination,selecting different intensities of light to direct towards at least oneof the first and second mold members, and then directing the differentintensities of ultraviolet light towards different portions of at leastone of the first and second mold members.
 94. The method of claim 1,further comprising directing rays of ultraviolet light through anannular gasket to cure the lens forming material.
 95. The method ofclaim 12, further comprising directing rays of ultraviolet light throughan annular gasket to cure the lens forming material.
 96. The method ofclaim 1 wherein the cavity defines a theoretical lens curvature that isdifferent from the desired curvature, and further comprising directingultraviolet rays towards at least one of the first and second moldmembers such that portions of the material in the cavity receivedifferent intensities of ultraviolet light from other portions of thematerial in the cavity, thereby allowing the material to cure to form alens with the desired curvature.
 97. The method of claim 16 wherein thecavity defines a theoretical lens curvature that is different from thedesired curvature, and further comprising directing ultraviolet raystowards at least one of the first and second mold members such thatportions of the material in the cavity receive different intensities ofultraviolet light from other portions of the material in the cavity,thereby allowing the material to cure to form a lens with the desiredcurvature.
 98. The method of claim 16, further comprising cooling thematerial in the lens cavity by directing air at a temperature of between0°-15° C. towards at least one of the first and second mold memberswhile substantially simultaneously directing ultraviolet rays towards atleast one of the first and second mold members.
 99. The method of claim16 wherein the mold cavity is substantially cylindrical and the heightof the cavity varies across the diameter of the cavity, and wherein theintensity of the ultraviolet rays is varied approximately in proportionto the height of the cavity.
 100. The method of claim 16 wherein thefirst and second mold members each have a face, and air is directedtoward the face of the first mold member, and toward the face of thesecond mold member.
 101. The method of claim 16 wherein the first andsecond mold members each have a center and edges, and air is directedfrom the edges of the first mold member to the center of the first moldmember.
 102. The method of claim 16 wherein the first and second moldmembers each have a center and edges, and air is directed from thecenter of the first mold member to the edges of the first mold member.103. The method of claim 16 wherein the ultraviolet light is filteredsuch that different intensities of it are applied to different portionsof the material in the cavity.
 104. The method of claim 103 wherein theultraviolet light is filtered with a filter which comprises a disk ofopaque material for reducing the intensity of ultraviolet light reachingthe center of the mold members relative to the intensity of ultravioletlight reaching the edge of the mold members during use.
 105. The methodof claim 103 wherein the ultraviolet light is filtered with a filterwhich comprises a transparent sheet material having a plurality ofultraviolet light absorbing shapes printed thereon.
 106. The method ofclaim 16 wherein the air is directed through a distributor whichcomprises an air jet having a substantially cylindrical bore, and thebore has a plurality of openings disposed about the circumferencethereof.
 107. The method of claim 106 wherein the average diameter ofthe openings in the air jet varies about the circumference of the bore.108. The method of claim 16, further comprising directing secondultraviolet rays towards the lens, thereby forming a lens with a seconddesired curvature.
 109. The method of claim 16, further comprisingdemolding and heating the lens.
 110. The method of claim 16, furthercomprising heating the lens to a temperature of about 65°-180° C. forless than about 30 minutes.
 111. The method of claim 16, wherein thematerial comprises at least one polyethylenic-functional monomercontaining two ethylenically unsaturated groups selected from acrylyland methacrylyl.
 112. The method of claim 111 wherein the materialfurther comprises an aromatic containing bis(allyl carbonate)-functionalmonomer.
 113. The method of claim 16, further comprising selecting thefirst mold and the second mold such that the cavity defines atheoretical curvature which, when the ultraviolet light is directed atthe material, will cause the material to form a lens with the desiredcurvature.
 114. The method of claim 113 wherein portions of the materialin, the cavity receive different intensities of ultraviolet light fromother portions of the material in the cavity, thereby causing thematerial to cure to form a lens with the desired curvature.